websockets.legacy is deprecated & is responsible for a large amount of start-up import latency

[fmmoret]

On my slow cloud VM, the imports caused by the legacy modules cost ~20% of my import time for uvicorn along the start-up critical path.
Uvicorn uses a mix of the legacy & non-legacy imports.

Here's a screenshot of the offending legacy imports

I don't know how much the alternative non-legacy paths would save, but hopefully there is more module cache overlap amongst the solely non-legacy modules

[fmmoret]

self time | cum time
via PYTHONPROFILEIMPORTTIME=1 & starting up uvicorn w/ a fast api app.