Fix TypeError in _process_path for curved elements simplification

Refactored the line simplification in _process_path to avoid the numpy TypeError caused by changing data-type for an object array. Replaced np.array(LineString(line).simplify(tolerance=quantization)) with separate LineString simplification and conversion of its 
coordinates to a numpy array. This ensures the correct handling.

vpype/io.py

@@ -336,7 +336,8 @@ def _process_path(path):
                 line = seg.npoint(np.linspace(0, 1, step))
 
                 if simplify:
-                    line = np.array(LineString(line).simplify(tolerance=quantization))
+                    line = LineString(line).simplify(tolerance=quantization)
+                    line = np.array(line.coords, dtype=float)
 
                 line = line.view(dtype=complex).reshape(len(line))