Drop bleak_scanner_instance; construct BleakScanner internally

[bdraco]

bleak removed register_detection_callback, so the detection callback must now be passed via the BleakScanner constructor. There is no way to add it after construction, so accepting an already-built scanner no longer works.

Drop the bleak_scanner_instance parameter from Controller and BleController entirely and always construct BleakScanner(detection_callback=self._device_detected) internally in BleController.async_start. Also drop the now-unused register_detection_callback(None) call from async_stop.

This is safe for Home Assistant because habluetooth already overwrites BleakScanner by the time we construct it, so the internally-created scanner is the HA-managed one.

This is a breaking change to the Controller signature, but it is forced by the upstream bleak removal; there is no compatible alternative.

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 75.13%. Comparing base (48b0280) to head (63db32d).

Files with missing lines	Patch %	Lines
aiohomekit/controller/ble/controller.py	12.50%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #552      +/-   ##
==========================================
- Coverage   75.21%   75.13%   -0.09%     
==========================================
  Files         100      100              
  Lines        9580     9563      -17     
==========================================
- Hits         7206     7185      -21     
- Misses       2374     2378       +4     

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