Don't persist known bad room state from /state_ids

[kegsay]

If we are told the state before event E is S via /state_ids, we should refuse to persist E if we fail to persist all events in S, else we are knowingly diverging from that server.

This causes room state to diverge on bad federation connectivity.

Discovered via Chaos testing.

Pending Complement tests.

Pull Request Checklist

• Pull request is based on the develop branch
• Pull request includes a changelog file. The entry should:
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[reivilibre]

Seems reasonable, but would indeed be nice to see a Complement test for this if you have the chance — feels like a subtle yet potentially severe case.