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.

Dockerfile.test

@@ -0,0 +1,14 @@
+FROM python:3.10-slim
+
+WORKDIR /app
+
+RUN apt-get update && \
+    apt-get install -y --no-install-recommends libgl1 libglib2.0-0 && \
+    rm -rf /var/lib/apt/lists/*
+
+COPY requirements-test.txt .
+RUN pip install --no-cache-dir -r requirements-test.txt
+
+COPY . .
+
+CMD ["python", "-m", "pytest", "tests/", "--tb=short", "--junitxml=/app/test-results/test-results.xml", "-q"]