Factorize protocol crypto operations

[jpraynaud]

Issue

We need to factorize the code that implements the protocol operations: key registration, clerk generation, ...

To do

• Create a common Protocol Key Registration Builder
• Create a common Protocol Clerk Builder (compute avk, create multi-signature, verify single signature)
• Create a common Protocol Initializer Builder (create single signature)
• Use these new builders in:
  • Aggregator: multi-signer
  • Signer: single-signer
  • Common: test setup of crypto helpers
  • Common: MithrilStakeDistribution of entities (compute next_aggregate_verification_key) (see Refactor MithrilStakeDistribution entity #967)

Ideas

Identify parts of crypto code that can be factorized between signer / aggregator / tests (see https://github.com/input-output-hk/mithril/blob/main/mithril-common/src/crypto_helper/tests_setup.rs#L105)