feat: Add onSelectionChange event for native text selection detection

[yacinebaroudi]

Summary

Adds native onSelectionChange event to UITextView component, enabling real-time text selection detection without polling.

Motivation

React Native's default Text component doesn't support text selection on iOS. The UITextView component provides native selection UI, but there was no way to detect when selection changes. This feature enables:

• Real-time selection detection
• Instant UI updates when text is selected
• Elimination of polling overhead (500ms intervals → instant events)
• Better performance and user experience

Changes

Native (iOS)

• Conformed RNUITextView to UITextViewDelegate protocol
• Implemented textViewDidChangeSelection: delegate method
• Emits onSelectionChange events via React Native event emitter
• Added error handling and debug logging

TypeScript

• Added SelectionChangeEvent interface to RNUITextViewNativeComponent.ts
• Added onSelectionChange prop to NativeProps
• Wrapped event handler in useCallback in Text.tsx for performance
• Added comprehensive JSDoc documentation

Documentation

• Updated CHANGELOG.md with feature description
• Added usage examples in README.md

Testing

• ✅ Tested in production app
• ✅ Verified with Arabic (RTL) text (multibyte characters)
• ✅ Tested rapid selection changes
• ✅ Confirmed no performance regressions
• ✅ Verified error handling works correctly

## Usage Example

import { UITextView } from 'react-native-uitextview';

function MyComponent() {
  const handleSelectionChange = (event: {
    nativeEvent: { target: number; start: number; end: number }
  }) => {
    const { start, end } = event.nativeEvent;
    console.log(`Selection: ${start}-${end}`);
  };

  return (
    <UITextView
      uiTextView={true}
      selectable={true}
      onSelectionChange={handleSelectionChange}
    >
      Selectable text content
    </UITextView>
  );
}

Breaking Changes

None. This is a purely additive feature.

[dr-contributor]

will this feature be added to the library?
will this functionality be extended to android as well?