feat: Expose NewDefaultPermutation in Poseidon2 packages

[Tabaie]

For use as a compression function and not a range-extended hasher

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Note

Expose NewDefaultPermutation across Poseidon2 packages and switch Merkle–Damgård hashers to use it; add SetBytesCanonical property tests and koalabear Poseidon2 test vectors.

• Poseidon2:
  • Add NewDefaultPermutation() returning Permutation{GetDefaultParameters()} in poseidon2.go for multiple curves/fields and update NewMerkleDamgardHasher() to use it.
  • Adjust hasher buffer sizing to derive from permutation params; update generator templates accordingly.
• Tests:
  • Add property-based test: SetBytesCanonical(Bytes()) remains constant in fp/fr element tests across curves and in field generator templates.
  • Add koalabear Poseidon2 test vectors (poseidon2/test-vectors.json) and vectors_test.go validating width, block sizes, and output.

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