[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.

Start by reviewing the firebase_admin package and reproducing the reported Mypy import-untyped warning. Determine the scope of type hints or package typing metadata needed, then verify that Mypy recognizes the package without the warning.】【。

Written by the indexing model from the issue text.