[Quant] Move to packed_modules_mapping from class var to instance var

[kylesayrs]

Purpose

• Move to packed_modules_mapping from class var to instance var to avoid potentially unintentional sharing of class var value

Changes

• Add initialization of packed_modules_mapping to __init__ function

Testing

• Find all instances of QuantizationConfig subclasses using grep -Er 'class\s+\w+\s*\(\s*QuantizationConfig\s*\)\s*:' vllm

[github-actions]

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[mgoin]

Nice, LGTM!

[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @kylesayrs.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork

[mgoin]

The failing test is due to guided decoding CI issues

[kylesayrs]

Implemented by #13104