Cleanup timelockId on execution for gas refund

[Amxx]

When calling execute, the state is checked. We expect to be in Queued. That means the state call done by execute is going to read _timelockIds[proposalId] and check the operation status. This sload makes the slot "hot".

As a consequence, cleaning it will cost 2900 and refund 4800, resulting in a theoretical 1900 gas savings. Because of the hash necessary to compute storage slot, this saving is reduced to 1825, which is still "nice to have".

• This does not change the behavior of the state(uint256) function
  • execute() sets the executed flag, which means the state will be returns without even looking at _timelockIds[proposalId]
• This does not change the behavior of the proposalEta(uint256) function
  • before this change, calling proposalEta on an executed proposal would lookup the deadline on the timelock. That returns _DONE_TIMESTAMP (1) which is rewritten to 0 by the governor
  • after this change, calling proposalEta on an executed proposal would lookup the deadline of 0x0 on the timelock, which should be 0.

PR Checklist

• Tests
• Documentation
• Changeset entry (run npx changeset add)

[changeset-bot]

🦋 Changeset detected

Latest commit: 830920a

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
openzeppelin-solidity	Minor

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[Amxx]

[Amxx]

With the reordering

[frangio]

This looks good, but there is a conflict that needs to be resolved.