refactor: prune orphaned attic modules and standardize project configurations

- Move orphaned modules (data_segment.py, contour_models.py, marching_squares.py) to attic/.
- Standardize local settings logic, serial port parameters, and graph view plots.
- Update pyproject.toml pyside6-project dependencies and configure gitignore.

src/pygui/backend/visualization/__init__.py

@@ -1,5 +1,4 @@
 # ===== Visualization Sub-package =====
-from pygui.backend.visualization.contour_models import ContourLine, ContourSegment
 from pygui.backend.visualization.graph_view import GraphView
 from pygui.backend.visualization.rbf_heatmap import interpolate_field
 from pygui.backend.visualization.wafer_map_item import WaferMapItem
@@ -7,5 +6,4 @@ from pygui.backend.visualization.wafer_map_item import WaferMapItem
 __all__ = [
     "WaferMapItem", "GraphView",
     "interpolate_field",
-    "ContourLine", "ContourSegment",
 ]