Add `granian` as a supported ASGI server

[hingebase]

granian

• is cross-platform (edit: now there is winloop)
• has better performance than uvicorn (but ~20% slower than fastwsgi whose ASGI support is unavailable on PyPI yet)
• is more actively maintained (edit: uvicorn is more active in 2026)

Roadmap:

• Switch between granian and uvicorn in mahoraga.toml to test their performance
• Support both of them as long as they're still maintained, and there is no one with dominant performance
• Drop one of them eventually