A preferences manager across platforms

Three files, three jobs:

• core/domain — the interface. Feature code depends on this and nothing else.
• core/data — the implementation. The only place the storage library is imported, and the only place key names exist.
• core/data/<platform> — the store instance. An expect fun returning the store, whose actuals each contain only a file path — construction is delegated to one shared function.

// commonMain — shared creation, one line per platform below it
fun createDataStore(producePath: () -> String): DataStore<Preferences> =
    PreferenceDataStoreFactory.createWithPath(produceFile = { producePath().toPath() })

expect fun createDataStoreInstance(): DataStore<Preferences>