Feat: Add user library endpoint and unofficial user token support

[daimoxd]

Description:

This pull request introduces the Library endpoint ( /v1/me/library ) to access the
user's authenticated content (albums, playlists, songs) and adds unofficial user
token authorization header management.

Changes:

• src/endpoints/Library/index.ts : Implements the LibraryEndpoint with getAlbums ,
getPlaylists , and getSongs fetching capabilities.
• src/AppleMusic.ts : Integrates the library endpoint property and handles its
initialization on init() .
• src/utils/Config.ts & src/utils/AxiosManager.ts : Adds support for custom
userToken configuration and injects the Music-User-Token header automatically when
AuthType.UserTokenUnofficial is active.
• src/index.ts : Exports LibraryEndpoint globally.
• src/endpoints/Library/index.test.ts : Unit test suite achieving 100% test coverage
on library requests.

Examples of usage:

import { AppleMusic, AuthType } from "@syncfm/applemusic-api";

const client = new AppleMusic({
  authType: AuthType.UserTokenUnofficial,
  userToken: "YOUR_MUSIC_USER_TOKEN_HERE"
});

await client.init();

// Fetch personal library items
const librarySongs = await client.Library.getSongs(25, 0);
console.log("Songs:", librarySongs);

const libraryAlbums = await client.Library.getAlbums(10, 0);
console.log("Albums:", libraryAlbums);