Stabilize conflicting modules warning

[konstin]

We added a check to warn when packages write to the same modules (#13437), causing broken installations and uninstallations. Specifically, this can cause non-deterministically broken installation that are inscrutable to users. This was reverted to preview (#15253).

• How to work with OpenCV 4 different installation methods? #10708
• Problem with opencv-python-headless installed via uv but not via pip #11806
• differences between pip & uv for opencv #11659
• Nondeterministic behavior of uv pip #13435
• Github action installation differs from local #13550
• Handling of different packages with same name (Pillow and Pillow-SIMD) is confusing. #14030
• uv sync removes necessary dependencies when two packages include the same module #15238
• Better support for conflicting transitive dependencies #15813

Note: If you are affected and need to remove one of two conflicting packages from your resolution, you can use an override with:

foo-wrong; sys_platform == "never"

Problems that need to be addressed before stabilization. Most of them can be solved by ignoring exact duplicates.

• [BUG]: Creating an env using uv v0.8.7 issues a warning NVIDIA/NeMo-Agent-Toolkit#611: This is a packaging bug and should be fixed upstream, neither of those packages should provide a tests module. Nevertheless, it's a useless warning to show.
• Warning that PySide6 is provided by more than one package since uv 0.8.7 #15239: Filed upstream as https://bugreports.qt.io/browse/PYSIDE-3161. The files are identical, so we can skip warning them. We'll still create a broken uninstallation when remove pyside6 alone, but it's not broken on installation.
• Older nvida-*-cu12 package have a redundant __init__.py (Warning that PySide6 is provided by more than one package since uv 0.8.7 #15239 (comment))
• [SETUP-BUG] mlflow, mlflow-skinny and mlflow-tracing contain duplicate files mlflow/mlflow#17267

[zanieb]

Thank you for writing up a tracking issue!