Clarify visualize error handling

[wshlavacek]

Summary

• remove the print-and-reraise fallback path in BNGVisualize
• centralize visualization execution / collection so cwd restoration happens in one place
• re-raise real BNGErrors cleanly and wrap filesystem failures as BNGFileError
• add focused regression coverage in tests/test_visualize_errors.py

Why

The current code mixes logging, print(...), and exception handling in a way that makes visualization failures noisier and less explicit than they need to be.

Testing

• uv run python -m pytest -q tests/test_visualize_errors.py
• uvx black --check bionetgen/core/tools/visualize.py tests/test_visualize_errors.py