fx quant: add typing for fuser (#48844)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/48844
Add types to function I/O for `Fuser` to improve readability
Test Plan:
```
mypy torch/quantization/
```
Imported from OSS
Reviewed By: jerryzh168
Differential Revision: D25337314
fbshipit-source-id: e5074d71c7834f24975169d36bf49357e53650ff
