feat: reverse mutations generation, mutations serialization (#355)

* feat: revert mutations generation, mutations serialization
* tests: check both `apply_mutations` and `apply_mutations_with_reversion`
* feat: add `num_leaves` method for `Smt`
* refactor: improve ad-hoc benchmarks
* chore: update crate version to v0.13.1

src/merkle/index.rs

@@ -128,7 +128,7 @@ impl NodeIndex {
         self.value
     }
 
-    /// Returns true if the current instance points to a right sibling node.
+    /// Returns `true` if the current instance points to a right sibling node.
     pub const fn is_value_odd(&self) -> bool {
         (self.value & 1) == 1
     }