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`

Another batch of `loot-core` migrated.

*  (prettier) adding trailing commas

* More commas

* style: enforce sorting of imports

* style: alphabetize imports

* style: merge duplicated imports