Refactor constants management to use Pydantic BaseModel for configuration

- Replaced module-level path variables in constants.py with a structured Pydantic Config class.
- Updated all relevant modules (train.py, augmentation.py, exports.py, dataset-visualiser.py, manual_run.py) to access paths through the new config structure.
- Fixed bugs related to image processing and model saving.
- Enhanced test infrastructure to accommodate the new configuration approach.

This refactor improves code maintainability and clarity by centralizing configuration management.

docker-compose.test.yml

@@ -0,0 +1,11 @@
+services:
+  test-runner:
+    build:
+      context: .
+      dockerfile: Dockerfile.test
+    volumes:
+      - ./test-results:/app/test-results
+      - ./_docs/00_problem/input_data:/app/_docs/00_problem/input_data:ro
+    environment:
+      - PYTHONDONTWRITEBYTECODE=1
+      - PYTHONUNBUFFERED=1