feat(qa): tune quality QA generation and compare prompts

[lipikaramaswamy]

Context

From e2e testing:

• Quality QA questions occasionally ask multiple things in one question, conflating multiple meaning units. This makes the compare step unfairly strict.
• Quality compare sometimes penalizes generalized answers that preserve core meaning but differ in specificity from the original QA answer.

Scope

• Prompt-tune meaning unit extraction and/or quality QA generation to produce single-focus questions
• Guide the quality compare prompt to treat generalized-but-correct answers as matching
• Measure impact on utility scores across bio and legal datasets

Files

• src/anonymizer/engine/rewrite/qa_generation.py (QA generation prompts)
• src/anonymizer/engine/rewrite/evaluate.py (compare prompt).

[lipikaramaswamy]

i think these issues on duplicates will go away when we use stronger models like qwen / minimax / maybe super