Made contextlib private in ScrollableContainers namespace (#25)

Allows wildcard imports of everything available in the package.

Author: tfpf

src/ScrollableContainers/__init__.py

@@ -1,10 +1,10 @@
-import contextlib
+import contextlib as _contextlib
 
-with contextlib.suppress(ImportError):
+with _contextlib.suppress(ImportError):
     from ScrollableContainers._qt5 import ScrollableAreaQt5
-with contextlib.suppress(ImportError):
+with _contextlib.suppress(ImportError):
     from ScrollableContainers._qt6 import ScrollableAreaQt6
-with contextlib.suppress(ImportError):
+with _contextlib.suppress(ImportError):
     from ScrollableContainers._tk import ScrollableFrameTk
-with contextlib.suppress(ImportError):
+with _contextlib.suppress(ImportError):
     from ScrollableContainers._wx import ScrollablePanelWx