Increase timeout tests delay and use uvicorn

[anuraaga]

Hopefully fixes #44

• Raise timeout from 1 -> 50. 1 is short enough that it can timeout even before the headers are prepared in CI bottlenecks
• I'm not sure but think there can be cases causing flakiness because the single-threaded wsgiref server hasn't cancelled the pending request yet before the next test. I switched it to uvicorn since it's easy to start programmatically and wouldn't have such an issue. Will revisit if we see flake still