fix gguf issue in alg_ext.py

[wenhuach21]

Description

Please briefly describe your main changes, the motivation.

Type of Change

• Bug fix
• New feature
• Documentation update
• Performance improvement
• Code refactoring
• Other (please specify):

Related Issues

Fixes or relates to #

Checklist Before Submitting

• My code has been tested locally.
• Documentation has been updated as needed.
• New or updated tests are included where applicable.

[Copilot]

Pull request overview

This PR updates the algorithm extension utilities in auto_round/alg_ext.py, primarily adjusting masking logic for loss computation and refining the iterative WLS quantization search rounding behavior.

Changes:

• Tweaks the top-percent absolute value mask selection logic line (no functional change intended, but exposes a doc/behavior mismatch).
• Adds the rounding perturbation term v into the quant_data_new computation inside iterative_wls_quant_search.