Custom font

Would it be possible to give users the option to not depend on the `Roboto-Regular.ttf` font?

Currently it looks like the font gets always added through the pubspec file.

```yml
flutter:
fonts:
- family: Roboto
fonts:
- asset: assets/fonts/Roboto-Regular.ttf
```

Start by inspecting pubspec.yaml and locating how the package references the Roboto-Regular.ttf asset. Determine how the font dependency can become optional, then verify that users can use the package without the bundled font while existing font behavior remains available.

Written by the indexing model from the issue text.