CoreBluetooth: pending operation futures dropped without reply on services-modified/clear

[qdot]

Several CoreBluetooth code paths drop pending operation futures without replying, so the awaiting caller hangs forever:

• on_services_modified (src/corebluetooth/internal.rs ~L788) and on_discovered_services (~L859) replace/clear p.services, discarding every characteristic's read/write/notify queues and descriptor queues (including an already-submitted setNotifyValue). on_discovered_services building characteristics from an empty map also defeats the in-flight preservation added for Race condition causes panic on subscription in CoreBluetooth #167 in set_characteristics.
• ClearPeripherals (~L1723) and the dead-sender eviction paths (~L741/761/777) drop the whole PeripheralInternal without calling drain_pending_operations.

Fix direction: drain (reply with an error to) pending futures before discarding services/peripherals, and preserve existing ServiceInternal/CharacteristicInternal state on re-discovery where the UUID still exists.