This pull request refactors the platform-specific GATT characteristic and service classes for BlueZ DBus, CoreBluetooth, and WinRT backends to use the unified BleakGATTCharacteristic and BleakGATTService base classes from bleak.backends.characteristic and bleak.backends.service. It removes backend-specific Bleak imports and updates the initialization and attribute management for improved compatibility and maintainability. The changes also add or update properties and methods for characteristic/service metadata and descriptor management.

Refactoring for Bleak compatibility and codebase simplification:

• All backend-specific characteristic classes (BlessGATTCharacteristicBlueZDBus, BlessGATTCharacteristicCoreBluetooth, BlessGATTCharacteristicWinRT) now inherit from the unified BleakGATTCharacteristic instead of backend-specific Bleak classes, and their constructors and init methods are updated to set attributes expected by Bleak. [1] [2] [3]
• All backend-specific service classes (BlessGATTServiceBlueZDBus, BlessGATTServiceCoreBluetooth) now inherit from the unified BleakGATTService, and their constructors and init methods are updated to set attributes expected by Bleak. [1] [2]

Characteristic and service metadata/property improvements:

• Added or updated properties for service_uuid, service_handle, handle, properties, descriptors, max_write_without_response_size, description, and uuid to all characteristic classes for consistency and Bleak compatibility. [1] [2] [3]
• Added or updated properties for description, characteristics, and uuid to service classes, including new methods for adding and retrieving characteristics and descriptors. [1] [2]

Descriptor and characteristic management:

• Added internal lists and methods to manage descriptors and characteristics (add_descriptor, get_descriptor, add_characteristic, get_characteristic) for both characteristics and services, improving extensibility and backend compatibility. [1] [2] [3] [4]

Initialization and attribute assignment updates:

• Initialization logic in all characteristic and service classes now sets backend-specific objects and attributes (obj, path, _service_uuid, _handle, _max_write_without_response_size, etc.) directly, removing legacy Bleak-specific initialization and simplifying attribute management. [1] [2] [3] [4] [5]

Removal of legacy and backend-specific Bleak imports:

• Replaced imports from backend-specific Bleak modules with imports from the unified bleak.backends.characteristic and bleak.backends.service modules, reducing code duplication and improving maintainability. [1] [2] [3] [4] [5]