Add NUMBER_OF_INPUTS to poseidon-proof

[0xjei]

Related Issue

Closes #116

Does this introduce a breaking change?

• Yes
• No

Other Information

This PR introduces the use of digest to compute the nullifier output signal instead of the preimage as specified in the #116.

Note that the number of constraints for NUMBER_OF_INPUTS = 1 is the same as in the previous implementation. As this number increases, the complexity of the circuit increases.

The @zk-kit/poseidon-proof package will be updated accordingly.

Todos

• Update the 'getArtifacts' methods based on the number
  of inputs.
• Update the 'circomkit' configuration to support 'scope'
  as a public signal.
• Bug: In the 'poseidon-proof' package, 'digest' and 'nullifier' are inverted in the return of the 'generate' method.
• Generate artifacts for a different number of inputs (1 <= noi
  <= 16).
• Make 'verification-keys.json' support the corresponding key per input (matrix for 'vk_delta_2' and
  'IC').
• Add missing tests.
• Update remote artifacts @cedoor

[cedoor]

Great job, just a few corrections in the comments!

[0xjei]

Converted to draft to make changes to @zk-kit/poseidon-proof before merging this feature.

[0xjei]

Ready for review @cedoor

[cedoor]

Great job @0xjei! Just a small fix for a bug that was already there before your PR.