[CPU] Introduce Int4WoqCpuTensor to replace Int4CPULayout in AQT

[Xia-Weiwen]

Summary
This PR adds Int4WoqCpuTensor to replace the AQT tensor with Int4CPULayout since AQT will be deprecated.

Test plan

pytest -sv test/quantization/quantize_/workflows/int4/test_int4_woq_cpu_tensor.py

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/ao/2798

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[Copilot]

Pull Request Overview

This PR introduces Int4WoqCpuTensor as a replacement for AQT tensor with Int4CPULayout to support int4 weight-only quantization on CPU with groupwise quantization.

Key changes:

• Adds new Int4WoqCpuTensor class for CPU-specific int4 weight-only quantization
• Integrates the new tensor type into the quantization API and workflow system
• Adds comprehensive test coverage for the new tensor implementation

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
torchao/quantization/quantize_/workflows/int4/int4_woq_cpu_tensor.py	Implements the core Int4WoqCpuTensor class with CPU-optimized int4 quantization
torchao/quantization/quantize_/workflows/init.py	Adds export for the new tensor class
torchao/quantization/quantize_/common/packing_format.py	Adds INT4_WOQ_CPU packing format enum value
torchao/quantization/quant_api.py	Integrates new tensor into quantization workflow
torchao/quantization/init.py	Adds public API export for the tensor class
test/quantization/quantize_/workflows/int4/test_int4_woq_cpu_tensor.py	Comprehensive test suite for the new tensor implementation

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