feat: modern transitions (zoom, adaptive), synchronized back gestures, and 0.2.0 release

[3d24rd0]

Summary of Changes

1. Modern & Synchronized Pop Gestures

• CupertinoBackGestureDetector: Implemented a pure widgets.dart gesture detector with full NavigatorState.didStartUserGesture() and NavigatorState.didStopUserGesture() synchronization.
• Configurable Gesture Region: Added backGestureWidth and popClosePercentage to PageTraceRoute and TraceRoute.page. Allows full-screen back swipe (backGestureWidth: null) or edge-only gesture (backGestureWidth: 20.0) to avoid conflicting with horizontal PageView, sliders, or carousels.

2. Modern Transitions in Pure widgets.dart

• Material 3 Zoom Transition (RouteTransition.zoom): Implemented Android 10+ / Material 3 style zoom and fade transition (incoming scale 0.85 -> 1.0 + fade in; outgoing scale 1.0 -> 1.08 + fade out).
• Platform-Adaptive Transition (RouteTransition.adaptive): Adaptively resolves to native transitions depending on the target platform:
  • iOS / macOS: SlideBuildTransition (Slide with parallax, edge shadow, and interactive gesture).
  • Android: ZoomBuildTransition (Material 3 Zoom & Fade).
  • Web / Desktop (Linux/Windows): FadeBuildTransition (Clean fade for desktop & SPA web).
• Refined Slide Transition (Slide): Removed card corner deformation (BorderRadius.circular(60)), added vertical leading edge shadow, and secondary route scrim barrier darkening for realistic depth.

3. Argument Safety & Stability

• Added guard in getAndClean to avoid unnecessary map mutations when the requested argument is not present.

4. Tests & Quality

• Added unit and widget test suites for CupertinoBackGestureDetector (test/cupertino_back_gesture_test.dart) and all transition widgets (test/transitions_test.dart).
• Total: 32/32 tests passing.
• Analyzer: 0 issues (coolint: ^3.0.0-rc.1).
• Package: 0 warnings on dart pub publish --dry-run.
• Bumped version to 0.2.0 and updated CHANGELOG.md and README.md.