fix: merkle store panics on bounds

Prior to this commit, the MerkleStore panicked under certain bounds. It
will prevent such panics by using checked operations.

ilog2, for instance, will panic when the operand is zero. However, there
is a documentation rule enforcing the merkle tree to be size at least 2.
If this rule is checked, then the panic is impossible.

src/merkle/mod.rs

@@ -35,7 +35,7 @@ pub use store::MerkleStore;
 // ERRORS
 // ================================================================================================
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, PartialEq, Eq)]
 pub enum MerkleError {
     ConflictingRoots(Vec<Word>),
     DepthTooSmall(u8),