Warn on deprecated CooperativeGroup alignment argument

[xiufanl]

Summary

• Emit a DeprecationWarning when the deprecated alignment argument is passed to cutlass.pipeline.CooperativeGroup.
• Add focused regression coverage for the deprecated positional argument and invalid thread-group size behavior.

Rationale

Some downstream examples and integrations still call CooperativeGroup(agent, size, alignment). Keeping the argument accepted while warning provides a migration path instead of failing at runtime.

Testing

• python -m py_compile test\python\CuTeDSL\test_pipeline_helpers.py
• git diff --check

The focused runtime unittest was not run locally because this checkout does not have the built cutlass._mlir extension installed.