Refactor utils/test.py: multi-path support, error handling, modular transforms

[Apprentice2907]

Fixes #124

What was changed

Only utils/test.py was modified. No other files touched.

Why

The original script had a hardcoded path, no error handling, commented-out
transforms, and would crash if a directory or file was missing. This made it
unreliable across different machines and environments.

Changes made

Multiple dataset paths

• Removed hardcoded root_dir
• Added --data_dirs CLI argument that accepts one or more paths
• All three DeepLense dataset paths are set as defaults

Error handling

• Script no longer crashes if a directory doesn't exist — it logs a warning and skips
• np.load() is wrapped in try/except to handle missing or corrupted .npy files
• Index is clamped to valid range instead of raising IndexError

Modular transforms

• Removed commented-out transform code
• Added build_transforms() function — crop size and normalize are now CLI flags
• Easy to extend without touching core logic

Reproducibility

• Added --seed, --index, --crop_size, --normalize, --output_dir CLI flags
• Same command produces same output on any machine

Output handling

• plots/ directory is created automatically if it doesn't exist
• Output filename includes dataset name and index to avoid silent overwrites

Code structure

• All logic moved into functions with a proper main() entry point
• Script is now importable and testable

How to run

default (uses all 3 DeepLense paths, index 50)

python utils/test.py

custom

python utils/test.py --data_dirs ../Data/real_lenses_dataset/lenses --index 10
python utils/test.py --crop_size 128 --