quant: enable mypy on torch/quantization/fx (#48331)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/48331
Enables mypy to not ignore type errors in FX quantization files. Fixes the easy
typing errors inline, and comments out the harder errors to be fixed at a later time.
After this PR, mypy runs without errors on `torch/quantization`.
Test Plan:
```
> mypy torch/quantization/
Success: no issues found in 25 source files
```
Imported from OSS
Reviewed By: jerryzh168
Differential Revision: D25133348
fbshipit-source-id: 0568ef9405b292b80b3857eae300450108843e80
