fix(pathfinder): satisfy mypy no-any-return in canary helpers

pre-commit.ci mypy flagged returning Any from resolve_ctk_root_via_canary and
_resolve_ctk_root_via_canary (both declared -> str | None), because
derive_ctk_root resolves to Any under the pathfinder mypy config. Bind the
result to an annotated local before returning, matching the pattern used
elsewhere in the package.

Author: aryanputta

cuda_pathfinder/cuda/pathfinder/_binaries/find_nvidia_binary_utility.py

@@ -72,7 +72,8 @@ def _resolve_ctk_root_via_canary() -> str | None:
     """
     from cuda.pathfinder._dynamic_libs.load_nvidia_dynamic_lib import resolve_ctk_root_via_canary
 
-    return resolve_ctk_root_via_canary(_CTK_ROOT_CANARY_ANCHOR_LIBNAME)
+    ctk_root: str | None = resolve_ctk_root_via_canary(_CTK_ROOT_CANARY_ANCHOR_LIBNAME)
+    return ctk_root
 
 
 def _resolve_in_trusted_dirs(normalized_name: str, dirs: list[str]) -> str | None:

cuda_pathfinder/cuda/pathfinder/_dynamic_libs/load_nvidia_dynamic_lib.py

@@ -148,7 +148,8 @@ def resolve_ctk_root_via_canary(canary_libname: str) -> str | None:
     canary_abs_path = _resolve_system_loaded_abs_path_in_subprocess(canary_libname)
     if canary_abs_path is None:
         return None
-    return derive_ctk_root(canary_abs_path)
+    ctk_root: str | None = derive_ctk_root(canary_abs_path)
+    return ctk_root
 
 
 def _try_ctk_root_canary(ctx: SearchContext) -> str | None: