collection: performance: use optimized parts function

Time: 8.53s => 5.73s

src/_pytest/python.py

@@ -41,6 +41,7 @@ from _pytest.mark.structures import get_unpacked_marks
 from _pytest.mark.structures import normalize_mark_list
 from _pytest.mark.structures import transfer_markers
 from _pytest.outcomes import fail
+from _pytest.pathlib import parts
 from _pytest.warning_types import PytestWarning
 from _pytest.warning_types import RemovedInPytest4Warning
 
@@ -562,14 +563,10 @@ class Package(Module):
             yield Module(init_module, self)
         pkg_prefixes = set()
         for path in this_path.visit(rec=self._recurse, bf=True, sort=True):
-            # We will visit our own __init__.py file, in which case we skip it.
-            if path.isfile():
-                if path.basename == "__init__.py" and path.dirpath() == this_path:
-                    continue
 
-            parts = path.parts()
+            parts_ = parts(path.strpath)
             if any(
-                pkg_prefix in parts and pkg_prefix.join("__init__.py") != path
+                pkg_prefix in parts_ and pkg_prefix.join("__init__.py") != path
                 for pkg_prefix in pkg_prefixes
             ):
                 continue