Allow player + save debounced updates to be handled synchronously

[tudddorrr]

Debounced API base class

• Introduced TaloDebouncedAPI, a reusable base class for APIs that need debounced batched updates with per-call result tracking, flush support, and queuing of updates that arrive while one is in-flight.

Player and save APIs return update results

• PlayersAPI and SavesAPI now extend TaloDebouncedAPI instead of managing their own debounce timers. debounce_update() returns a Signal that resolves with a PlayerUpdateResult or SaveUpdateResult, letting callers await the outcome of a specific debounced operation (e.g. to inspect rejected props).
• New player_updated and save_updated signals notify listeners when debounced updates settle.

Prop mutation methods now return values

• set_prop, delete_prop, set_prop_array, delete_prop_array, insert_into_prop_array, and remove_from_prop_array on EntityWithProps and Player changed return type from void to Variant, returning a signal/awaiter when an update is queued so callers can chain await on the result.

Graceful flush on quit

• TaloManager._handle_quit() now flushes pending debounced player and save updates before exiting, preventing data loss from in-flight or queued updates at shutdown.

Debounce timer stop support

• DebounceTimer gained a stop() override that clears the pending flag, enabling flush_updates() to force-immediate execution of queued work.