Pyrefly extensions

[connernilsen]

If we were to add a Pyrefly extensions package, what functionality would we consider providing? This isn't necessarily an indication we plan on doing this soon or are promising any specific features, but I want to get a place to consolidate ideas so that we can evaluate it in the future.

[connernilsen]

One idea from #5521 is to add a Protocol class that ABCs or other metaclasses can diamond inherit from without causing runtime errors in Python.

Other broken typing features or extensions to typing welcome!