fix(contract): cancel in-flight rounds on vote_deactivate quorum (#186)

[jeffrey701]

Summary

When a miner is deactivated via quorum the closure only flips miner_active and emits the event. Any REQ_ACTIVATE / REQ_RESERVE / REQ_INITIATE round already in flight stays voteable, so a later vote reaching its own quorum can run its closure against a now-deactivated miner. do_initiate is the most consequential one — its closure did not re-read miner_active.

Two changes in smart-contracts/ink/lib.rs:

1. vote_deactivate quorum closure calls clear_request(miner, REQ_*) for each miner-keyed request type after deactivation, so any pending vote rounds for that miner stop being countable.
2. The REQ_INITIATE consensus closure re-checks miner_active at closure time and returns Error::MinerNotActive on miss. Belt and suspenders against a same-block race where a deactivation and an initiate-quorum vote land in the same block.

REQ_RESERVE already gates at entry; the entry-point check is sufficient given the new clear_request call in vote_deactivate.

Test plan

• Existing contract tests pass
• Manual: vote_deactivate quorum followed by a delayed vote on a pre-existing REQ_INITIATE round — the late vote should not find the request (cleared) and the closure should never run.
• Manual: same-block race — a REQ_INITIATE quorum vote and a vote_deactivate quorum vote land in the same block — initiate closure returns MinerNotActive if deactivation lands first.

Closes #186