Add AccessorySetupKit support on iOS

[fotiDim]

Summary

• add an iOS 18+ AccessorySetupKit picker-and-connect API
• remove AccessorySetupKit-managed devices through the existing unpair API
• document the required Info.plist keys and asset setup
• regenerate platform bindings and return unsupported errors outside iOS

Tests

• dart analyze
• flutter test (110 tests)
• iOS simulator build with xcodebuild

Notes

• Android Gradle verification was blocked before source compilation because the local Flutter plugin loader rejects JDK 25.0.2.
• macOS verification was blocked because the example workspace Pods are out of sync.

Closes #219