Add TestRecursiveProofFixedSizeMerkleTree for recursive proof generation

[byksy]

Description

This pull request introduces a new test, TestRecursiveProofFixedSizeMerkleTree, to validate the correctness of the recursive proof generation in the FixedSizeMerkleTree. The test covers the creation of a Merkle tree with multiple leaves, selection of a specific leaf, generation of a Merkle proof using the recursiveProof method, and verification that the reconstructed Merkle root matches the original root of the tree.

Changes Made

• Added the TestRecursiveProofFixedSizeMerkleTree test function to the merkle_test.go file.
• Updated the introduction comment and provided a clear commit message for the new test.

Testing

• Ran the newly added test locally to ensure it passes.