feat(compat): add compatible command groups for legacy eras
- Add CompatibleGroup with era-specific wrappers (Shelley, Allegra, Mary, Alonzo, Babbage) - Implement StakeAddressGroup, StakePoolGroup, GovernanceGroup, and TransactionGroup for compatible commands - Refactor transaction building to avoid duplication: construct TxRawOutput in gen_signed_tx_bare - Move gen_pparams_update from GovernanceActionGroup to GovernanceGroup - Add Google-style docstrings to all compatible command functions - Fix linting errors: add type annotations and shorten long lines This enables generating legacy-era certificates and transactions that are expected to be rejected in the Conway era, useful for negative testing scenarios.