Defer import of Segmenter to speed up help message printing

Still allows Segmenter to be imported by a user, but bypasses its heavy imports until called directly

src/wing_segmenter/__init__.py

@@ -1,3 +1,7 @@
 __version__ = "0.1.0"
 
-from wing_segmenter.segmenter import Segmenter
+def __getattr__(name):
+    if name == 'Segmenter':
+        from wing_segmenter.segmenter import Segmenter
+        return Segmenter
+    raise AttributeError(f"module {__name__} has no attribute {name}")