Renders the native Unity container non-opaque on iOS so Flutter
widgets painted behind the platform view show through. Requires
the Unity camera's clear colour to use alpha 0.
- UnityConfig.transparentBackground (default false) + fullscreen factory override
- iOS UnityKitView recursively applies isOpaque=false and clear bg to Unity view hierarchy
- Android: flag ignored, warning logged via UnityKitLogger (iOS-only for now)
- UnityConfig.toString() now reports every field for parity with ==/hashCode
- Tests: defaults, copyWith, equality, hashCode, toString, factory override
- Bump to 1.1.0, CHANGELOG updated, README usage section added