Fix: pip requirements handling for environment-marker dependencies

[NeuralFault]

This fix resolves a shared Stability Matrix requirements-handling bug that was reported in two places: ComfyUI extension installs on the SM Discord, specifically for the ComfyUI_PuLID_Flux_ll extension, and the Wan2GP install failure I reproduced locally. In both cases, the underlying problem was the same: valid requirements.txt entries containing environment markers were being mangled before they reached uv pip install.

For the ComfyUI extension case, the affected line is the upstream dependency entry:
onnxruntime-gpu; sys_platform != 'darwin' and (platform_machine == 'x86_64' or platform_machine == 'AMD64')

For the Wan2GP case, the affected lines are the upstream Python-version-gated onnxruntime-gpu entries:
onnxruntime-gpu==1.22.0; python_version < "3.11"
and
onnxruntime-gpu==1.25.0.dev20260210001; python_version >= "3.11"

The fix updates Stability Matrix’s shared pip requirements argument handling so environment-marker dependencies are preserved as single install arguments, and corrects command-line quoting so embedded quoted marker values such as "3.11" are escaped properly instead of being stripped or split. Regression tests were added to verify that marker-bearing requirement lines survive both parsing and final command-string generation correctly.

[gemini-code-assist]

Code Review

This pull request updates the PipInstallArgs class to handle requirement entries more specifically by introducing the ToRequirementArgument method, which distinguishes between flags and standard requirements. It also adds a unit test to ensure that requirements with environment markers are correctly treated as single, quoted arguments. I have no feedback to provide.

[ionite34]

Thanks looks good