fix(sequencer): ensure sequencer cannot propose twice | graceful handling of non proposer in notice queue

[danwt]

Description

Does two things

1. Makes sure that we don't expect seqs in the notice queue to be the proposer. Since, we don't clear the queue on hard fork. This was correct before but I removed the required if recently, for some reason.
2. Check 'notice started' as potential proposer condition. It's actually needed to stop a proposer re-opting in after rotating out. As alternative solution, we could disable opt-in after notice started. I'm not bullish.

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Closes #XXX

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I have...

• Added a relevant changelog entry to the Unreleased section in CHANGELOG.md
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• Import/Export Genesis
• Registered Invariants
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[mtsitrin]

might be cleaner to just k.removeFromNoticeQueue(ctx, seq) when proposer forcibly rotated