[PyTorch] Optimize GroupedLinear validation

[negvet]

Description

Please include a brief summary of the changes, relevant motivation and context.

Fixes # (issue)

Type of change

• Documentation change (change only to the documentation, either a fix or a new content)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Infra/Build change
• Code refactoring

Changes

Please list the changes introduced in this PR:

• Change A
• Change B

Checklist:

• I have read and followed the contributing guidelines
• The functionality is complete
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[greptile-apps]

Greptile Summary

The PR avoids unnecessary backward custom-quantizer validation when gradients are disabled while preserving validation on the first grad-enabled use.

• Moves the grad-mode guard into _validate_custom_recipe_quantizers after built-in-recipe, missing-generation, and cache checks.
• Calls backward validation unconditionally from _get_quantizers, allowing the validator’s fast paths to avoid unnecessary grad-mode queries.
• Extends hybrid quantization tests for inference, cached validation, and the transition to grad-enabled execution.

Confidence Score: 5/5

The PR appears safe to merge.

No blocking failure remains.

Important Files Changed

Filename	Overview
transformer_engine/pytorch/module/grouped_linear.py	Defers backward custom-quantizer validation while gradients are disabled and retains validation before a backward-capable forward consumes the generation.
tests/pytorch/test_hybrid_quantization.py	Adds coverage for built-in recipes, no-grad initialization, first grad-enabled validation, and cached-validation fast paths.

_{Reviews (2): Last reviewed commit: "Merge branch 'main' into optimize_groupe..." | Re-trigger Greptile}

[vthumbe1503]

LGTM. Thanks for fixing the review comment from previous PR

[vthumbe1503]

/te-ci pytorch