refactor: Remove Firebase Core and Storage dependencies

[amaan-0331]

This commit removes all dependencies on Firebase Core and Firebase Storage.

Changes include:

• Removing firebase_storage from pubspec.yaml.
• Removing the DynamicCachedFonts.fromFirebase constructor and all related logic from lib/dynamic_cached_fonts.dart.
• Removing the handleUrl function and firebase_storage import from lib/src/utils.dart.
• Removing all Firebase-related tests and mock data from test/dynamic_cached_fonts_test.dart.
• Cleaning up the example directory by:
  • Removing firebase_core and firebase_storage from example/pubspec.yaml.
  • Deleting firebase_demo.dart, firebase_options.dart, and platform-specific Firebase configuration files.
  • Removing Firebase references from integration tests.

[sidrao2006]

Hi @amaan-0331, thanks for your interest in contributing to the project!

I would like the package to support fetching fonts from Firebase Cloud Storage directly, any reason you're proposing to remove this feature?

[amaan-0331]

Hey @sidrao2006, first of all, great work with the project.
I removed the firebase_storage dependency because the same functionality can be achieved using the existing fromUrl constructor (Firebase Storage already provides methods like getDownloadURL() to fetch a usable URL).

This avoids forcing all users of the package to pull in firebase_storage as a transitive dependency, which keeps the package lighter, reduces the chance of version conflicts, and makes the package more flexible for projects that aren’t using Firebase at all.