ENH: Enable relative import of Slicer Python-wrapped libraries

Improve the fallback mechanism in `slicer/__init__.py` to support relative import
of Slicer Python-wrapped libraries (kits) when they are distributed as standalone
Python packages (e.g., `slicer-mrml`).

This change allows importing modules using relative paths when absolute imports
fail, supporting package layouts like:

```
slicer_mrml/
  ├── __init__.py
  ├── vtkAddon/
  ├── vtkSegmentationCore.so
  └── qMRMLWidgetsPythonQt/
```

This makes it possible to use Slicer Python kits in isolated package distributions
outside the monolithic Slicer application structure.

Author: Thibault-Pelletier

Base/Python/slicer/__init__.py

@@ -194,7 +194,11 @@ def _createModule(name, globals, docstring):
     try:
         exec("from %s import *" % (kit))
     except ImportError as detail:
-        print(detail)
+        # Try kit relative import if installed in as a traditional package
+        try:
+            exec("from .%s import *" % (kit))
+        except ImportError:
+            print(detail)
 
     del kit