mypy

645ea62c - Reduce the size of the build by not compiling parts of stubgen (#10107)

Reduce the size of the build by not compiling parts of stubgen (#10107) This might fix the out-of-memory errors we are getting when building Windows wheels. In any case these will speed up builds slightly. The `stubgen.py` file must be compiled since it uses inheritance from native classes. This removes one case of inheritance, but the others are harder to get rid of.