Add descriptor read and write API

[rohitsangwan01]

Resolves: #250

[Copilot]

Pull request overview

This PR adds cross-platform support for reading and writing GATT characteristic descriptor values (e.g., 0x2901 / 0x2902) through the existing Universal BLE API surface, addressing Issue #250.

Changes:

• Adds new Pigeon/platform-interface APIs: readDescriptorValue / writeDescriptorValue, plus high-level UniversalBle.readDescriptor / UniversalBle.writeDescriptor.
• Implements descriptor read/write on Windows, Android, Darwin (iOS/macOS), Linux (BlueZ), and Web.
• Updates examples and tests to exercise descriptor read/write flows.

Reviewed changes

Copilot reviewed 20 out of 22 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
windows/src/universal_ble_plugin.h	Declares Windows plugin descriptor read/write methods.
windows/src/universal_ble_plugin.cpp	Implements Windows descriptor read/write via GATT descriptor APIs.
windows/src/generated/universal_ble.g.h	Updates generated Windows Pigeon interface with descriptor APIs.
windows/src/generated/universal_ble.g.cpp	Wires Windows message channels for descriptor read/write.
pigeon/universal_ble.dart	Adds descriptor read/write to the Pigeon definition.
lib/src/interfaces/universal_ble_platform_interface.dart	Extends platform interface with descriptor read/write.
lib/src/universal_ble.g.dart	Adds Dart-side generated channel calls for descriptor read/write.
lib/src/universal_ble_pigeon/universal_ble_pigeon_channel.dart	Implements descriptor APIs for the Pigeon-backed platform implementation.
lib/src/universal_ble.dart	Adds public UniversalBle.readDescriptor / writeDescriptor APIs with queueing/UUID parsing.
lib/src/universal_ble_web/universal_ble_web.dart	Implements Web descriptor read/write + descriptor lookup helper.
lib/src/universal_ble_linux/universal_ble_linux.dart	Implements BlueZ descriptor lookup + read/write.
android/src/main/kotlin/com/navideck/universal_ble/UniversalBle.g.kt	Updates generated Android Pigeon bindings for descriptor APIs.
android/src/main/kotlin/com/navideck/universal_ble/UniversalBleHelper.kt	Adds Android future types for descriptor read/write completions.
android/src/main/kotlin/com/navideck/universal_ble/UniversalBlePlugin.kt	Implements Android descriptor read/write and completion handling.
darwin/universal_ble/Sources/universal_ble/UniversalBle.g.swift	Updates generated Swift Pigeon bindings for descriptor APIs.
darwin/universal_ble/Sources/universal_ble/UniversalBleHelper.swift	Adds descriptor lookup helper and new “future” structs.
darwin/universal_ble/Sources/universal_ble/UniversalBlePlugin.swift	Implements Darwin descriptor read/write, including CCCD special handling.
test/universal_ble_test_mock.dart	Extends the platform mock surface with descriptor methods.
test/ble_characteristic_test.dart	Adds a test covering write/read descriptor behavior using mocks.
example/lib/data/mock_universal_ble.dart	Extends example mock with descriptor read/write.
example/lib/peripheral_details/widgets/services_list_widget.dart	Updates UI to surface descriptors and pass selected descriptor on taps.
example/lib/peripheral_details/peripheral_detail_page.dart	Adds example read/write descriptor UI and enables descriptor discovery.

Suppressed comments (1)

windows/src/universal_ble_plugin.cpp:654

• Error message has a typo ("devicesId") which is inconsistent with the rest of the API surface (deviceId) and leaks into user-facing errors.

      result(create_flutter_error(UniversalBleErrorCode::kDeviceNotFound,
                                  "Unknown devicesId:" + device_id));
      return;

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