[BUG][pathfinder] Windows system DLL search fails to load CUDA dependencies

[rwgk]

Summary

When CUDA DLLs are discovered via the Windows system search (PATH), the initial DLL can be found, but its co-located dependencies fail to load. This shows up as error 126 during LoadLibraryExW and breaks the pathfinder fallback on Windows systems without CUDA_HOME/CUDA_PATH configured.

Problem

• The current pathfinder Windows logic calls LoadLibraryExW with flags=0 after finding a CUDA DLL on PATH.
• Windows loads the target DLL, but does not search the DLL's directory for it dependencies, so dependency resolution fails (error 126).
• This prevents loading NVRTC and related CUDA DLLs for users who rely on PATH instead of CUDA_HOME or CUDA_PATH.

Why this went unnoticed

• Our Windows test environments always have CUDA_HOME or CUDA_PATH set.
• That means the PATH-based fallback path is rarely exercised, so dependency load failures did not surface in CI or local testing.

Proposed fix (WIP)

• WIP PR [pathfinder] Use LOAD_WITH_ALTERED_SEARCH_PATH for system DLL search on Windows #1506 switches to SearchPathW to resolve the full DLL path and then uses LoadLibraryExW(..., LOAD_WITH_ALTERED_SEARCH_PATH) so dependency search starts in the DLL's directory.

References

• Context: discovered while testing suggested code for Use pathfinder for dynamic libraries numba-cuda#308