Upgrade deps for react 19 support

[RogierKonings]

Upgrade to React 19 Support

This PR adds official support for React 19 while maintaining backward compatibility with React 16.8.0+.

Changes

• Updated peer dependencies to support React 19.x (< 21 instead of < 20)
• Fixed build configuration for modern Node.js ES modules
• Added "type": "module" to package.json
• Updated rollup.config.js with proper JSON import assertions

Compatibility

• All existing code is fully compatible with React 19
• No breaking changes required in source code
• useState, useEffect, and useRef hooks work correctly
• IntersectionObserver usage follows React 19 best practices

Testing

• Build completes successfully without errors or warnings
• TypeScript compilation passes with @types/react ^19.2.2
• All hooks and patterns validated against React 19 documentation

This is a non-breaking change for consumers of this library.