[Dev] Support device-initiated grouped linear without TE op fuser

[lhb8125]

Summary

• Port [Main] Support device-init grouped linear module too with when not using TE opfuser #6000 from main to dev.
• Enable Transformer Engine's device-initiated GroupedLinear/GroupedTensor path when the TE operation fuser is disabled.
• Preserve device-side expert token metadata to avoid the legacy .tolist() host synchronization.
• Add grouped weight/bias handling, dispatcher padding support, configuration validation, and numerical coverage.

This PR is the prerequisite for #6845 and should be merged first.

Dependency

• Improve device-init grouped linear module with single grouped weight support  TransformerEngine#3224.

Test plan

• CHECK_ONLY=true BASE_REF=dev ... bash tools/autoformat.sh (Black, isort, pylint, and ruff passed).
• python tools/check_copyright.py <changed Python files>.
• python -m py_compile on all changed Python files.
• Full PyTorch/Transformer Engine tests are left to upstream CI because the local lightweight environment does not include PyTorch.

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