Improve exception handling - replace generic Exception with specific types

[chelslava]

Summary

Replaces generic Exception catches with more specific exception types throughout the codebase.

Changes

• dataloader.py: Use specific exception types
• libraryfinder.py: Use specific exception types
• fileexplorerplugin.py: Use specific exception types
• notebook.py: Use specific exception types
• eventhandler.py: Use specific exception types

This improves error handling and makes debugging easier.