stdlib: Use protocols instead of IO for GZipFile

[jlost]

Kicking this problem upstream: #5099

GzipFile is still using IO as argument type, which is discouraged. We prefer custom protocols for argument types, and that would hopefully fix the problem above.

Does it make sense to use custom protocols in GZipFile? Would it be an improvement?

[JelleZijlstra]

Yes, this is the direction we want in general. You don't necessarily need custom protocols; it's possible that something like _typeshed.SupportsWrite will suffice (I haven't checked).

[srittau]

What Jelle said. Please ignore the word "custom" in my quote above. That said, this is just a duplicate of #5099.