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/attic/contour_models.py

@@ -0,0 +1,26 @@
+from dataclasses import dataclass, field
+from typing import List
+
+
+# ===== Single Contour Segment =====
+@dataclass
+class ContourSegment:
+    start_x: float
+    start_y: float
+    end_x: float
+    end_y: float
+
+    @property
+    def start(self):
+        return (self.start_x, self.start_y)
+
+    @property
+    def end(self):
+        return (self.end_x, self.end_y)
+
+
+# ===== Contour Line =====
+@dataclass
+class ContourLine:
+    level: float
+    segments: List[ContourSegment] = field(default_factory=list)