[huangji6693-max]

Summary

• Remove the strict signer-index ordering check (current_index <= last_index) in governance::approve() that permanently deadlocked proposals whenever a higher-index signer approved before a lower-index signer.
• Preserve duplicate-approval rejection (GovError::AlreadyApproved), signer membership validation (GovError::NotASigner), and stake-gate checks.
• Add regression test out_of_order_approval_still_reaches_threshold verifying that a 2-of-3 multisig reaches quorum when signer index 2 approves before signer index 1.

Verification

running 12 tests
test governance::tests::out_of_order_approval_still_reaches_threshold ... ok
test governance::tests::threshold_transition_sets_unlock ... ok
...
test result: ok. 12 passed; 0 failed; 0 ignored; 0 measured

Closes #176