Refactor Quantizer for reusing in QAT
Could you demostrate/link how do you want to use that refactored `Quantizer`?
 Note that changes will need to be unstreamed to another project as well here https://github.com/NVIDIA/NeMo-Framework-Launcher/blob/main/launcher_scripts/conf/ptq/model/quantization.yaml. I think we'll need to chop this slightly > Could you demostrate/link how do you want to use that refactored `Quantizer`?

Its used in https://github.com/NVIDIA/NeMo/pull/9276 We'll need to do follow up MRs to:
* https://github.com/NVIDIA/NeMo-Framework-Launcher/blob/main/launcher_scripts/conf/ptq/model/quantization.yaml 
* https://github.com/NVIDIA/TensorRT-Model-Optimizer/blob/main/llm_ptq/nemo_ptq.py
(I know it's duplication but it is what it is) @janekl should I rename `alpha` to `sq_alpha` so it is clear alpha is used only for SQ? > @janekl should I rename `alpha` to `sq_alpha` so it is clear alpha is used only for SQ?

OK, good idea (same applies to Launcher ofc.)
# What does this PR do ?

This PR refactors the Quantizer class used for PTQ so it can be reused for QAT as well (follow-up PR)

Note that functionally wise it is same as before

**Collection**: N/A

# Changelog 
- N/A

# Usage

- N/A

# GitHub Actions CI

The Jenkins CI system has been replaced by GitHub Actions self-hosted runners.

The GitHub Actions CI will run automatically when the "Run CICD" label is added to the PR.
To re-run CI remove and add the label again.
To run CI on an untrusted fork, a NeMo user with write access must first click "Approve and run".

# Before your PR is "Ready for review"
**Pre checks**:
- [x] Make sure you read and followed [Contributor guidelines](https://github.com/NVIDIA/NeMo/blob/main/CONTRIBUTING.md)
- [ ] Did you write any new necessary tests?
- [x] Did you add or update any necessary documentation?
- [x] Does the PR affect components that are optional to install? (Ex: Numba, Pynini, Apex etc)
  - [ ] Reviewer: Does the PR have correct import guards for all optional libraries?
  
**PR Type**:
- [ ] New Feature
- [ ] Bugfix
- [ ] Documentation
- [x] Refactoring existing feature code

If you haven't finished some of the above items you can still open "Draft" PR.


## Who can review?

Anyone in the community is free to review the PR once the checks have passed. 
[Contributor guidelines](https://github.com/NVIDIA/NeMo/blob/main/CONTRIBUTING.md) contains specific people who can review PRs to various areas.

# Additional Information
* Related to # (issue)
