321 bn254mimc test vector

[Tabaie]

Simple test vector generator for MiMC - BN254.

Possible other features:

• Include result by round (or every 10 rounds so that the test entries are smaller)
• Include test cases with custom string input (conventionally hashed to fr first)

[gbotrel]

looks good, may be worth it to have at least one vector that takes multiple elements as input. I believe the intended use case is state manager so I hear "merkle tree path" 👍