feat: NativeScript with Angular renderer + client app

[NathanWalker]

NativeScript renderer for A2UI

• Added the @a2ui/nativescript package
• Implemented core data processing logic in src/lib/data/processor.ts via the MessageProcessor service, which manages surfaces, processes messages, and handles event dispatching for NativeScript
• Documentation included here
• Demo mode included to explore as mentioned here

nativescript-a2ui-native-ios-and-android.mp4