Fix memory leaks in AppStateListener and Room

[viachaslauinnowise]

Fix: memory leaks in AppStateListener observers and Room cleanup

AppStateListener:

• Store NotificationCenter observer tokens for proper cleanup
• Add deinit to remove all observers
• Use [weak self] in all observer closures

Room:

• Remove from AppStateListener.delegates in deinit (safety net)
• Explicitly remove in cleanUp() (primary path)
• Prevent memory leaks when Room is destroyed without cleanUp()

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[pblazej]

Can you explain why this is needed if AppStateListener uses:

private struct State {
  let delegates = NSHashTable<AnyObject>.weakObjects()
}

[pblazej]

This is a singleton, so where the removal will occur?

[pblazej]

As you see in the other PR(s) there's ongoing work to improve Swift concurrency and memory management in general, so thank you for bringing this topic.

However, this PR:

• does not provide any evidence that such leaks occur
• breaks reconnection semantics (as AppStateListener is added on init but removed during cleanup() now)
• abuses deinit introducing unsafe unowned

If we want to introduce some best practices here, we can try modernizing AppStateListener by leveraging Combine observers (AsyncStream is supported in iOS 15).

Otherwise, I'd suggest closing this PR.