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/__init__.py

@@ -7,7 +7,6 @@ from pygui.backend.controllers.session_controller import SessionController  # no
 from pygui.backend.data.csv_file_metadata import CSVFileMetadata  # noqa: F401
 from pygui.backend.data.csv_recorder import CsvRecorder  # noqa: F401
 from pygui.backend.data.data_records import read_data_records  # noqa: F401
-from pygui.backend.data.data_segment import DataSegment  # noqa: F401
 from pygui.backend.data.file_browser import FileBrowser  # noqa: F401
 from pygui.backend.data.local_settings import LocalSettings  # noqa: F401
 from pygui.backend.data.local_settings_model import LocalSettingsModel  # noqa: F401
@@ -19,7 +18,6 @@ from pygui.backend.models.sensor_editor import SensorEditor  # noqa: F401
 from pygui.backend.models.session_model import SessionModel  # noqa: F401
 from pygui.backend.models.stability_detector import StabilityDetector  # noqa: F401
 from pygui.backend.models.threshold_classifier import ThresholdConfig  # noqa: F401
-from pygui.backend.visualization.contour_models import ContourLine, ContourSegment  # noqa: F401
 from pygui.backend.visualization.graph_view import GraphView  # noqa: F401
 from pygui.backend.visualization.rbf_heatmap import interpolate_field  # noqa: F401
 from pygui.backend.visualization.wafer_map_item import WaferMapItem  # noqa: F401