fix: add /usr/local/cuda fallback for CTK header discovery

When `CUDA_PATH`/`CUDA_HOME` are unset, fall back to `/usr/local/cuda`
on non-Windows platforms. Aligns with CuPy's `get_cuda_path()` behavior
and fixes CuPy header detection in containers (e.g. Holoscan).

Ref: PR #956

Author: jcfr

cuda_pathfinder/cuda/pathfinder/_headers/find_nvidia_headers.py

@@ -107,6 +107,11 @@ def _find_ctk_header_directory(libname: str) -> LocatedHeaderDir | None:
         if result := _locate_based_on_ctk_layout(libname, h_basename, cuda_home):
             return LocatedHeaderDir(abs_path=result, found_via="CUDA_HOME")
 
+    # Fallback: typical system install path (matches CuPy's get_cuda_path())
+    if not IS_WINDOWS and os.path.exists('/usr/local/cuda'):
+        if result := _locate_based_on_ctk_layout(libname, h_basename, '/usr/local/cuda'):
+            return LocatedHeaderDir(abs_path=result, found_via="system_default")
+
     return None