Wormhole Core Contract Fixes

[dkgoutham]

Summary

Implements all 11 fixes from Wormhole team review feedback on the Stellar core contract.

1. Trailing bytes check — All four governance payload parsers now reject payloads with extra bytes after parsing, matching EVM/Solana behavior.
2. CurrentGuardianSetIndex TTL — set_current_index now extends TTL on write, preventing the contract from becoming non-functional if the entry gets archived.
3. Remove StorageKey::Admin — Removed dead admin storage key and its write in initialization; Soroban's update_current_contract_wasm doesn't use it.
4. Remove governance_emitter storage — Getter now returns the GOVERNANCE_EMITTER const directly; constructor validates the param matches the const instead of persisting it.
5. MessageFee TTL on read — post_message_with_fee now extends the MessageFee TTL when fee is non-zero, preventing silent fallback to free messaging.
6. Eliminate double VAA parsing in governance — verify_and_hash_governance_vaa now calls verify_vaa_signatures directly instead of verify_vaa, which was internally re-parsing the VAA.
7. Fix is_governance_vaa_consumed return type — Changed from Result<(), WormholeError> to Result<bool, WormholeError>; errors are now reserved for parse failures only.
8. Add parse_and_verify_vaa — New combined trait method and implementation matching EVM's parseAndVerifyVM; verify_vaa now delegates to it internally.
9. VAA version check — VAA::try_from now rejects VAAs with version != 1, matching EVM.
10. Remove MINIMUM_CONTRACT_BALANCE — Removed the 1 XLM minimum balance check from transfer_fees; Soroban contracts cannot be deallocated for having zero XLM.
11. Remove TTL extension from consume_vaa — Persistent storage archival already provides replay protection; the extend_ttl was unnecessary cost.