[FR] Missing type hints

**Is your feature request related to a problem? Please describe.**
Mypy is reporting:
```
Skipping analyzing "firebase_admin": module is installed, but missing library stubs or py.typed marker
Mypy[import-untyped](https://mypy.readthedocs.io/en/latest/_refs.html#code-import-untyped)

See https://mypy.readthedocs.io/en/stable/running_mypy.html#missing-imports
Mypy[note](https://mypy.readthedocs.io/en/stable/running_mypy.html#missing-imports)
```

**Describe the solution you'd like**
I would like Mypy to be able to provide valid type hints and stop warning me that it can't.

**Describe alternatives you've considered**
Use ` # type: ignore` to ignore the warning.