[Python][Annotations] Add pyrefly check to CI

[rok]

Describe the enhancement requested

Add pyrefly type check to the CI.
See also #49102 and #48622 (comment)

Component(s)

Python

[rok]

cc @samwgoldman

[jorisvandenbossche]

Is it needed to add yet another type checker? (the more type checkers, the more maintenance effort to keep them all happy)
I find https://pyrefly.org/blog/too-many-type-checkers/ an interesting resource, which essentially says it is fine to run just one type checker on your code, but run multiple on the tests (as a way to test your public API with as many type checkers as possible, but for internal development just choose one).

I know we don't yet actually run the type checkers on the code (or tests, since those directories are excluded), but something to think about for when are planning to enable this.

[rok]

@jorisvandenbossche that approach seems reasonable. Also I suppose work on the annotations will show how problematic multi-typechecker setup would be. And I suppose we can postpone any decisions until then.