Dedup code in connection state update.

[leoyvens]

Deduplicate and refactor code in State.update. The method is now more concise. Formatted with rustfmt because I got lazy to format it manually, but I may do that if it is preferable.

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[seanmonstar]

Great! I'll look it over more closely a bit later, as this method is tricky/dangerous.

[seanmonstar]

This is excellent, thank you!