Mark distutils as `py.typed`

[Avasam]

I thought this wouldn't do anything shipped as a setuptools submodule, but it turns out pyright does understand it as it needs to support py.typed in submodules for namespace packages:

The spec isn't completely clear here. But for type-checkers that understand it: it's a benefit. And for those that don't, nothing changes.

I think distutils/compilers is considered a namespace package, hence the need for the second py.typed

Without:

With: