Add TypeScript type definitions

[ingadi]

Description
This pull request adds TypeScript type definitions enabling full type safety and autocompletion features when using this library in TypeScript projects.

Changes made

1. Added index.d.ts:

• Created type definitions for all exported functions and interfaces

2. Type definitions:
   Interfaces:

• Options
• GetSongByIdOptions
• Song

Functions:

• getLyrics
• getSong
• searchSong
• getSongById
• getAlbumArt

3. Updated package.json:

• Added "types": "index.d.ts" to enable TypeScript support.

Testing:

• Verified type definitions in a local TypeScript project.

Conclusion:
These additions enhance the library's usability for TypeScript developers.