add Poseidon implementation over bn254

[HSG88]

Description

This PR adds support for Poseidon hash over the scalar field of BN254, Poseidon has better performance compared to MiMC and is being used in multiple projects.

Fixes #494

Type of change

• [*] New feature (non-breaking change which adds functionality)
• [*] This change requires a documentation update

How has this been tested?

All unit tests have been made according to the code referenced in Poseidon paper page 20 footnote 16.

How has this been benchmarked?

The code hasn't been benchmarked yet.

Checklist:

• [*] I have performed a self-review of my code
• [*] I have commented my code, particularly in hard-to-understand areas
• [*] New and existing unit tests pass locally with my changes

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[ivokub]

Sorry for the delay - we have merged Poseidon2 permutation #553 recently. Would that be satisfiable? Even though it doesn't implement full hash function, then in many use cases (particularly in SNARK circuits where we hash only fixed number of inputs) it is not necessary.

If you would still be interested in contributing this PR, then we would need to have code-generated implementation for all curves.