dbr quant: clean up key types in AutoQuantizationState mappings (#68369)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/68369
`AutoQuantizationState` has various mappings keyed on IDs. Only
`tensor_id_to_observer` actually needs string keys because it is an
`torch.nn.ModuleDict`. This PR changes the other mappings to have
integer keys, for simplicity and performance.
Test Plan:
```
python test/test_quantization.py TestQuantizeDBR
```
Reviewed By: jerryzh168
Differential Revision: D32463765
Pulled By: vkuzo
fbshipit-source-id: 5a9bf2a1102859097eedf1e536761084cd408856
