pub.dev score: license, dartdoc, analysis, tests

- Add MIT license
- Add dartdoc to all public APIs (UxKeyboard, BendBox, Bezier, Json)
- Add analysis_options.yaml with flutter_lints and public_member_api_docs
- Add repository, issue_tracker, topics to pubspec.yaml
- Expand package description
- Fix BendBox constructor (const, super.key)
- Remove unused import in keyboard.dart
- Replace boilerplate tests with UxKeyboard smoke tests
- Move ux dependency to example's dependencies (not dev_dependencies)

example/.flutter-plugins-dependencies

@@ -1 +1 @@
-{"info":"This is a generated file; do not edit or check into version control.","plugins":{"ios":[{"name":"ux","path":"/Users/agra/projects/ux/","native_build":true,"dependencies":[],"dev_dependency":true}],"android":[{"name":"ux","path":"/Users/agra/projects/ux/","native_build":true,"dependencies":[],"dev_dependency":true}],"macos":[],"linux":[],"windows":[],"web":[]},"dependencyGraph":[{"name":"ux","dependencies":[]}],"date_created":"2026-04-15 13:13:36.363037","version":"3.41.5","swift_package_manager_enabled":{"ios":false,"macos":false}}
+{"info":"This is a generated file; do not edit or check into version control.","plugins":{"ios":[{"name":"ux","path":"/Users/agra/projects/ux/","native_build":true,"dependencies":[],"dev_dependency":false}],"android":[{"name":"ux","path":"/Users/agra/projects/ux/","native_build":true,"dependencies":[],"dev_dependency":false}],"macos":[],"linux":[],"windows":[],"web":[]},"dependencyGraph":[{"name":"ux","dependencies":[]}],"date_created":"2026-04-16 18:49:44.385595","version":"3.41.5","swift_package_manager_enabled":{"ios":false,"macos":false}}