Feat: GKR-Hashers

[Tabaie]

• Implements full hash functions for Poseidon2 and MiMC.
• Updates the Merkle Damgard hasher to implement the StateStorer interface.

Benchmark: For 27M constraints for 52K permutations on BLS12-377, using degree 17 gates. Attempts to use degree 2 and 4 gates proved counterproductive, resulting in 32M and 31M constraints, respectively.

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Note

Implements hashers built on GKR compressors and adds state management for Merkle–Damgård, with broad test/bench coverage and a small generated-code fix.

• Add GKR compressors for mimc and poseidon2 with gate registration per curve; cache compiled circuits via kvstore
• New std/hash/mimc/gkr-mimc and std/hash/poseidon2/gkr-poseidon2 providing full hashers (Merkle–Damgård) and end-to-end tests/benchmarks
• Update MerkleDamgardHasher: constructor returns StateStorer; add State()/SetState() with safety checks
• Refactor Poseidon2: export Parameters, add GetDefaultParameters, change New and registration to use StateStorer; update tests (including state restore)
• Minor fixes: correct gateAPI.Println type handling in generated GKR backends; comment typo in MiMC internals

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