[seemenkina]

Summary

• Decouple the consensus core from Ethereum-specific signing by introducing a single ConsensusSignatureScheme trait (identity + async sign + static verify) in src/signing.rs.
• ConsensusService<Scope, Storage, Event, Signer> now carries the scheme as a generic param via PhantomData; validate_proposal, validate_vote, and ConsensusSession helpers are generic over Signer.
• EthereumConsensusSigner wraps alloy::signers::local::PrivateKeySigner and is the default scheme used by DefaultConsensusService. Embedders can plug in Ed25519, HSM-backed signers, libchat accounts, or any other scheme.
• Sign/verify errors collapse into a single ConsensusSchemeError thiserror enum (Sign / Verify variants). ConsensusError::MismatchedLength and InvalidSignature are removed; scheme-level failures surface via ConsensusError::SignatureScheme(_).
• tests/custom_scheme_tests.rs exercises the generic path end-to-end with a non-Ethereum stub scheme, proving the abstraction holds.
• Bumps the crate to 0.3.0 with CHANGELOG migration notes and refreshed README.

Breaking change

cast_vote, build_vote, and validate_proposal now require a ConsensusSignatureScheme. Migrate by wrapping existing signers:

// before
service.cast_vote(&scope, id, true, private_key_signer).await?;

// after
use hashgraph_like_consensus::signing::EthereumConsensusSigner;
service.cast_vote(&scope, id, true, EthereumConsensusSigner::new(private_key_signer)).await?;

validate_proposal::<EthereumConsensusSigner>(&proposal)?; for direct callers.

Test plan

• cargo fmt --all --check
• cargo clippy --all-features --tests -- -D warnings
• cargo test --all-features --tests (all 91 tests pass, including the new custom_scheme_tests)
• cargo test --doc
• CI green