Fix bug which caused metric publishing to not accept query string parameters in ASGI app

[hacksparr0w]

The _bake_output function in exposition.py expects the params argument to be a dict[str, Any] but the ASGI interface does not handle encoding, thus the parameters are passed in as dict[bytes, Any].

[csmarchbanks]

Thanks! Would you be willing to write a test for this please? Or add enough type hinting that it would be caught by mypy.

[hacksparr0w]

I isolated the bug into a test case. Codifying this into type hints would be non-trivial since the used parse_qs function from urllib.parse is not typed and returns Any.

[csmarchbanks]

Thanks!