refactor(consensus): use TransactionRef in transaction-sync paths

[VorobyevIlya]

Description of change

Transaction-synchronization paths carried transaction identifiers as GenericTransactionRef, whose BlockRef arm exists only for CommitV1 — no longer produced, rejected from peers by commit-version verification, and absent from the per-epoch store. These paths therefore only ever see TransactionRef.

• Use TransactionRef directly in the transactions synchronizer, the network fetch request/service types, verify_transactions_with_transactions_refs, the serving path, and both commit syncers, converting once where refs enter from the still-generic core interfaces.
• The wire format is unchanged: refs were already serialized untagged and the server always parsed TransactionRef.
• BlockRef itself and the core-side uses of GenericTransactionRef are untouched.

Links to any relevant issues

fixes #12343

How the change has been tested

• Basic tests (linting, compilation, formatting, unit/integration tests)
• Patch-specific tests (correctness, functionality coverage)
• I have added tests that prove my fix is effective or that my feature works
• I have checked that new and existing unit tests pass locally with my changes