Pass on stm module

[iquerejeta]

Refactor of the library. Goal is to simplify the core-library in the next few iterations, and provide what is strictly required. This PR simplifies the crate, and in particular the stm module.

• StmSig does not require the Verification key + PoP, as in the registration PoP is already verified.
• PartyId is no longer linked to a signature.
• Introduced the StmAggrVerificationKey, which essentially is the root of the merkle tree and the full stake.
• Renamed StmMultiSig -> StmAggrSig to have a clearer distinction with the multi signature.
• Minor optimisation in StmAggrSig. Instead of individually verifying k signatures (= to evaluating k pairings), we first aggregate the signatures, and the keys, and verify the aggregate (= k additions in G1 and G2 and one pairing evaluation)
• Removed serialisation from ClosedRegistration, Signer and Clerk. This is intentional, to force generation of signers or clerks to produce an instance from valid keys (and their PoP).
• Removed C-API. We are expecting a lot of changes to the library, and not expecting to use it out of rust. A C-API may be useful in the future, but not now.
• Created a dense_mapping module to simplify the stm module (by far the most complex and crucial module of the library).
• Clerks no longer verify multi signatures. Instead, we have multi signatures capable of being verified provided a verification key. This allows for signature verification without the need to generating a Clerk.

[github-actions]

Unit Test Results

    5 files   - 1    14 suites   - 1   2m 19s ⏱️ -3s
113 tests  - 7  113 ✔️  - 7  0 💤 ±0  0 ❌ ±0 

Results for commit cf26c38. ± Comparison against base commit f20638e.

This pull request removes 9 and adds 2 tests. Note that renamed tests count towards both.

src/stm.rs - stm::StmSigner<D> ‑ new_epoch (line 634)
stm ‑ clerkFromPublicData
stm ‑ dynamicStake
stm ‑ failSigningIfIneligible
stm ‑ invalidRegistration
stm ‑ produceAndVerifyAggregateSignature
stm::tests ‑ test_clerk_serialize_deserialize
stm::tests ‑ test_precision_approximation
stm::tests ‑ test_signer_serialize_deserialize

dense_mapping::tests ‑ test_precision_approximation
src/stm.rs - stm::StmSigner<D> ‑ new_epoch (line 674)

♻️ This comment has been updated with latest results.