Add FlushUpdates and events for players/saves debounced updates

[tudddorrr]

Debounced API overhaul

• DebouncedAPI is now generic over TReturnData and TUpdateResult, enabling callers to receive typed results from debounced operations instead of fire-and-forget voids.
• Player.SetProp, DeleteProp, and their array variants now return Task<PlayerUpdateResult>, letting callers await the outcome and inspect rejected props inline.
• Talo.Saves.UpdateCurrentSave and DebounceUpdate now return Task<SaveUpdateResult> with the updated save on success.

Completion signals and flush support

• Added OnPlayerUpdated(bool) and OnSaveUpdated(bool, GameSave) events that fire after each debounced settle, so UI can react without polling.
• FlushUpdates() on both APIs drains any pending trailing calls and returns a FlushResult enum (NothingPending, Success, Failure).
• TaloManager.OnApplicationQuit now flushes events, player updates, and save updates before the process exits, preventing silent data loss.

Sample and documentation updates

• Playground SetProp sample now awaits the result and shows rejection reasons inline instead of relying on a global event listener.
• Saves demo subscribes to OnSaveUpdated for save feedback instead of manually toggling button text after awaiting.