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I've updated the return values in `sync/index` to sensible values based
on how they're being called.

I've updated the type of `msg.value` to be `string | number | null` to
match the values expected by `serializeValue`

This is the last PR with lots of renaming for `loot-core`!

*  (prettier) adding trailing commas

* More commas

* style: enforce sorting of imports

* style: alphabetize imports

* style: merge duplicated imports