Enable WASM-compat and monitor it in the CI (#142)

* fix: Use `target_pointer_size` conditional compilation

There are some parts of the code where is needed to de/serialze
`usize`s. These, have sizes that vary depending on the target
achitecture the code is compiled for.

Hence, this adapts the de/serialization to the specific pointer size for
which the crate is being compiled to.

* change: Support WASM-compatibility and polish Cargo.toml

In order to support Wasm-compat and to simplify and improve `Cargo.toml`
readability, the follwing changes have been made:

- All the deps that can use `parallel` feature, do so. As `rayon`
  supports non-threaded targets with a fallback option. See: https://docs.rs/rayon-core/1.12.1/rayon_core/index.html#global-fallback-when-threading-is-unsupported
- `ark-grumpking` has been brought to `0.5.0-alpha.0` as `0.4.0` appears
  to not be in `crates.io` anymore. See: https://crates.io/crates/ark-grumpkin/versions
- By default, the crate uses `"ark-circom/default"` which selects the
  `wasmer/sys` feature such that it knows where wasmer is
  suposed to be run`.
- Added a `wasm` feature which forces `ark-circom/wasm` to be used
  instead. Which internally selects the `wasmer/js` backend to be used
  such that in-browser execution is possible.
- Added `getrandom` with `js` feature as dependency when `wasm32-unknown-unknown` target is selected such
  that compilation of the crate for testing or simply building is possible. Notice that with `wasi` and other wasm targets,
  this is not the case as they're automatically supported.
  For more info, please check: https://docs.rs/getrandom/latest/getrandom/#webassembly-support

* feat: Support WASM-compatibility tests in CI

Add support for both testing the build of `sonobe/folding-schemes` for
WASM-targets and also, it's build as a dependency for a WASM-crate.

This includes a build job for the three main supported rust-WASM targets
and the same but for a thrid crate creted on-the-fly which uses
`sonobe/folding-schemes` as a dependency.

* chore: Add README docs about WASM-compat & feats

* ci: don't run WASM-compat job if PR is draft

* chore: depend on `arnaucube/circom-compat` fork.

Since https://github.com/arnaucube/circom-compat/pull/2 was merged, we
can already switch to it as we were depending before.

* chore: minimal build/test instructions

* fix: CI typos

* fix: Update CI to use correct feature sets

* fix: `ark-grumpkin` versioning issues

As mentioned in
https://github.com/privacy-scaling-explorations/sonobe/issues/146
there's a big issue that involves some dependencies of the crate.

As a temporary fix, this forces the workspace to rely on a
"non-existing" version of `ark-grumpkin` which is immediately patched at
workspace-level for a custom version that @arnaucube owns with some
cherry-picked commits.

While this allows the CI to pass and crate to build, a better solution
is needed.

* fix: Clippy CI avoiding --all-targets

* fix: use `wasm` feat only with folding-schemes

folding-schemes/Cargo.toml

@@ -4,25 +4,26 @@ version = "0.1.0"
 edition = "2021"
 
 [dependencies]
-ark-ec = "^0.4.0"
-ark-ff = "^0.4.0"
-ark-poly = "^0.4.0"
-ark-std = "^0.4.0"
-ark-crypto-primitives = { version = "^0.4.0", default-features = false, features = ["r1cs", "sponge", "crh"] }
-ark-grumpkin = {version="0.4.0"}
-ark-poly-commit = "^0.4.0"
+ark-ec = { version = "^0.4.0", default-features = false, features = ["parallel"] }
+ark-ff = { version = "^0.4.0", default-features = false, features = ["parallel", "asm"] }
+ark-poly = { version = "^0.4.0", default-features = false, features = ["parallel"] }
+ark-std = { version = "^0.4.0", default-features = false, features = ["parallel"] }
+ark-crypto-primitives = { version = "^0.4.0", default-features = false, features = ["r1cs", "sponge", "crh", "parallel"] }
+ark-grumpkin = { version = "0.4.0", default-features = false }
+ark-poly-commit = { version = "^0.4.0", default-features = false, features = ["parallel"] }
 ark-relations = { version = "^0.4.0", default-features = false }
-ark-r1cs-std = { version = "0.4.0", default-features = false } # this is patched at the workspace level
-ark-snark = { version = "^0.4.0"}
-ark-serialize = "^0.4.0"
-ark-circom = { git = "https://github.com/arnaucube/circom-compat" }
+# this is patched at the workspace level
+ark-r1cs-std = { version = "0.4.0", default-features = false, features = ["parallel"] }
+ark-snark = { version = "^0.4.0", default-features = false }
+ark-serialize = { version = "^0.4.0", default-features = false }
+ark-circom = { git = "https://github.com/arnaucube/circom-compat", default-features = false }
+ark-groth16 = { version = "^0.4.0", default-features = false, features = ["parallel"]}
+ark-bn254 = { version = "^0.4.0", default-features = false }
 thiserror = "1.0"
-rayon = "1.7.0"
+rayon = "1"
 num-bigint = "0.4"
 num-integer = "0.1"
 color-eyre = "=0.6.2"
-ark-bn254 = {version="0.4.0"}
-ark-groth16 = { version = "^0.4.0" }
 sha3 = "0.10"
 ark-noname = { git = "https://github.com/dmpierre/ark-noname", branch="feat/sonobe-integration" }
 noname = { git = "https://github.com/dmpierre/noname" }
@@ -44,18 +45,16 @@ rand = "0.8.5"
 tracing = { version = "0.1", default-features = false, features = [ "attributes" ] }
 tracing-subscriber = { version = "0.2" }
 
-[features]
-default = ["parallel"]
-light-test = []
+# This allows the crate to be built when targeting WASM.
+# See more at: https://docs.rs/getrandom/#webassembly-support 
+[target.'cfg(all(target_arch = "wasm32", target_os = "unknown"))'.dependencies]
+getrandom = { version = "0.2", features = ["js"] }
 
-parallel = [ 
-    "ark-std/parallel", 
-    "ark-ff/parallel",  
-    "ark-ec/parallel",  
-    "ark-poly/parallel", 
-    "ark-crypto-primitives/parallel",  
-    "ark-r1cs-std/parallel",  
-    ]
+[features]
+default = ["ark-circom/default", "parallel"]
+parallel = []
+wasm = ["ark-circom/wasm"]
+light-test = []
 
 
 [[example]]

folding-schemes/src/folding/hypernova/mod.rs

@@ -593,9 +593,21 @@ where
             return Err(Error::MaxStep);
         }
 
-        let mut i_bytes: [u8; 8] = [0; 8];
-        i_bytes.copy_from_slice(&self.i.into_bigint().to_bytes_le()[..8]);
-        let i_usize: usize = usize::from_le_bytes(i_bytes);
+        let i_usize;
+
+        #[cfg(target_pointer_width = "64")]
+        {
+            let mut i_bytes: [u8; 8] = [0; 8];
+            i_bytes.copy_from_slice(&self.i.into_bigint().to_bytes_le()[..8]);
+            i_usize = usize::from_le_bytes(i_bytes);
+        }
+
+        #[cfg(target_pointer_width = "32")]
+        {
+            let mut i_bytes: [u8; 4] = [0; 4];
+            i_bytes.copy_from_slice(&self.i.into_bigint().to_bytes_le()[..4]);
+            i_usize = usize::from_le_bytes(i_bytes);
+        }
 
         let z_i1 = self
             .F

folding-schemes/src/folding/nova/decider_eth.rs

@@ -201,7 +201,7 @@ where
         let (cmW_x, cmW_y) = NonNativeAffineVar::inputize(U.cmW)?;
         let (cmT_x, cmT_y) = NonNativeAffineVar::inputize(proof.cmT)?;
 
-        let public_input: Vec<C1::ScalarField> = vec![
+        let public_input: Vec<C1::ScalarField> = [
             vec![pp_hash, i],
             z_0,
             z_i,

folding-schemes/src/folding/nova/mod.rs

@@ -502,9 +502,22 @@ where
         if self.i > C1::ScalarField::from_le_bytes_mod_order(&usize::MAX.to_le_bytes()) {
             return Err(Error::MaxStep);
         }
-        let mut i_bytes: [u8; 8] = [0; 8];
-        i_bytes.copy_from_slice(&self.i.into_bigint().to_bytes_le()[..8]);
-        let i_usize: usize = usize::from_le_bytes(i_bytes);
+
+        let i_usize;
+
+        #[cfg(target_pointer_width = "64")]
+        {
+            let mut i_bytes: [u8; 8] = [0; 8];
+            i_bytes.copy_from_slice(&self.i.into_bigint().to_bytes_le()[..8]);
+            i_usize = usize::from_le_bytes(i_bytes);
+        }
+
+        #[cfg(target_pointer_width = "32")]
+        {
+            let mut i_bytes: [u8; 4] = [0; 4];
+            i_bytes.copy_from_slice(&self.i.into_bigint().to_bytes_le()[..4]);
+            i_usize = usize::from_le_bytes(i_bytes);
+        }
 
         let z_i1 = self
             .F