feat: add support for hashmaps in Smt and SimpleSmt (#363)

src/hash/rescue/rpo/digest.rs

@@ -1,5 +1,11 @@
 use alloc::string::String;
-use core::{cmp::Ordering, fmt::Display, ops::Deref, slice};
+use core::{
+    cmp::Ordering,
+    fmt::Display,
+    hash::{Hash, Hasher},
+    ops::Deref,
+    slice,
+};
 
 use thiserror::Error;
 
@@ -55,6 +61,12 @@ impl RpoDigest {
     }
 }
 
+impl Hash for RpoDigest {
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        state.write(&self.as_bytes());
+    }
+}
+
 impl Digest for RpoDigest {
     fn as_bytes(&self) -> [u8; DIGEST_BYTES] {
         let mut result = [0; DIGEST_BYTES];