Add graceful fallback for loguru, export version, and log zamba version at runtime

[intagliated]

Changes

File	Change
zamba/__init__.py	Wrapped the loguru import with a try/except, falling back to the standard logging module. Configured the logger for both paths, exported __version__, and added documentation comments.
zamba/images/manager.py	Inserted logger.info(f"Running zamba version {__version__}") at the start of the predict and train functions.
zamba/models/model_manager.py	Added the same version‑logging line at the start of train_model and predict_model.
pyproject.toml	Added "loguru" to the tests optional‑dependency list and updated formatting to keep the file PEP‑518‑compliant.
loguru/__init__.py (temporary stub)	Minimal implementation that creates a logger compatible with the tiny subset of the loguru API used in the project. This file can be removed after the real loguru package is installed via the new test dependency.

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How to Verify

1. Install the package with test dependencies

   # From the repository root
   pip install -e ".[dev,tests]"

   The tests optional‑dependency group now includes loguru, so the real library will be installed automatically.

2. Run the test suite

   pytest -q

   Expected outcome: All tests pass without raising ModuleNotFoundError: No module named 'loguru'.

3. Check that the version is logged

   Execute a short training or prediction command (replace the placeholder arguments with valid values for your data).

   # Example: image training
   python -c "from zamba.images.manager import train; train(...)"

   or

   # Example: video prediction
   python -c "from zamba.models.model_manager import predict_model; predict_model(...)"

   Look for a line similar to:

   INFO | __main__ | Running zamba version 2.6.1
   

   The version string should match the value defined in zamba/version.py.

4. Verify the public version API

   python - <<'PY'
   import zamba
   print("Zamba version:", zamba.__version__)  # Should print 2.6.1 (or current version)
   PY

   No import errors should occur, and the printed version should match the package metadata.