[Testing] MultisigGovernance ProposalIdMismatch and expire-on-cancelled branches are uncovered

[grantfox-oss]

Telegram (ask questions / claim the issue here first): https://t.me/+DOylgFv1jyJlNzM0

Why this matters

multisig_governance/src/lib.rs:485-487 returns GovernanceError::ProposalIdMismatch (4018) when emergency_cancel_proposal is called with a wrong id, and expire_proposal (519-537) returns ProposalNotActive for a cancelled proposal. multisig_governance/src/test.rs exercises emergency_cancel only with the correct id and never expires a cancelled proposal, so both branches have no test.

Acceptance criteria

• Test emergency_cancel_proposal with a non-matching proposal_id returns ProposalIdMismatch
• Test expire_proposal on a proposal that was already cancelled returns ProposalNotActive
• Test emergency_cancel_proposal is idempotent when called twice (second call returns Ok on an already-cancelled proposal)

Files to touch

• contracts/multisig_governance/src/test.rs

Out of scope

• Changing emergency-cancel or expiry semantics