fix: MerkleDamgardHasher IV

[Tabaie]

Fixes an incorrect IV initialization that would make the hash fail after a Reset.

[Copilot]

Pull Request Overview

This PR fixes a bug in the MerkleDamgardHasher where the IV was incorrectly re‐used on a reset, which could cause the hash to fail after a reset. The changes update the Reset method (using a safe clone of the IV), refactor state initialization via cloneLeftPadded, and add additional tests across multiple curve implementations to validate the fix.

Reviewed Changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated no comments.

File	Description
internal/generator/crypto/hash/poseidon2/template/poseidon2.test.go.tmpl	Added new tests and imports to validate the MerkleDamgardHasher functionality
hash/merkle-damgard.go	Updated Reset and SetState to clone the IV and refactored padding logic via cloneLeftPadded
ecc/*/fr/poseidon2/poseidon2_test.go	Added new tests (TestHashSmall and TestHashReset) across various ECC curves to verify correct hashing behavior

Comments suppressed due to low confidence (1)

hash/merkle-damgard.go:96

• Consider adding unit tests to verify the error handling in cloneLeftPadded when the input buffer length exceeds the expected size.

	if len(b) > n {