Fix LocalStorage observeChanges ignores later keys

[zry98]

Summary

In LocalStorageImpl.observeChanges, awaitClose was placed inside the keys.forEach loop, the coroutine suspended after the first iteration, so the listeners for the remaining keys were never registered. The first key was effectively the only one observed, changes to later keys are ignored silently.

This fix replaces the per-key listeners with a single listener that filters by the watched key set and registers/unregisters once.

Checklist

• New or updated tests have been added to cover the changes following the testing guidelines.
• The code follows the project's code style and best_practices.
• The changes have been thoroughly tested, and edge cases have been considered.
• Changes are backward compatible whenever feasible. Any breaking changes are documented in the changelog for users and/or in the code for developers depending on the relevance.

[TimoPtr]

Thanks for catching this 👍🏻 it is my mistake ...