Improve pytest parsing for beginner-friendly evaluation feedback

[NickK21]

Summary

• extracts pytest parsing into a dedicated parser
• preserves real pytest assertion, collection, and runtime messages instead of collapsing them into generic output
• normalizes failure targets and test names
• captures expected, received, and rawout in a more structured way
• codewit.us now depends on stable structured failure data to generate beginner-friendly Outcome messages
• fixes the old problem where useful pytest details were getting buried, truncated, or reduced to noisy output