test: add CPU-only unit coverage for sharding helpers

[Pritiks23]

Summary

• add unit tests for sharding utility internals in test/utils/test_sharding_unit.py
• validate marker argument parsing/defaulting/validation in mark_values
• validate context-aware predicate evaluation in params_in_context
• validate default SM inheritance/precedence behavior in DefaultSMs

Why

test/utils/test_sharding.py contains core test-selection logic used by pytest sharding flows, but helper-level behavior had no direct unit coverage. These tests harden that logic without requiring CUDA or GPU runtime.

Validation

• pytest -q test/utils/test_sharding_unit.py
• result: 8 passed

Notes

• CPU-only verification path
• no CUTLASS kernel behavior changes

[Pritiks23]

This PR adds CPU-only unit coverage for sharding helper logic used during pytest test selection, without changing any kernel/runtime behavior.

What is covered:

Marker argument parsing/defaulting/validation via mark_values
Parameter-context predicate evaluation via params_in_context
Default SM inheritance and nearest-scope precedence via DefaultSMs
Why this matters:

The sharding helper code influences which tests run or skip in CI
These paths were previously untested at helper-unit level
Added coverage reduces regression risk in test selection behavior and keeps verification possible without CUDA/GPU

[Pritiks23]

Hi maintainers — PR is ready for review. I’m happy to iterate on feedback.