Add general difflib reward function + format extraction task

[kalomaze]

Most of the time for this was spent on synthetic data creation + cleaning so far, reward func may need tweaking ideally.

Examples include:

• extraction w/ precise formatting requirements
• conditional instructions

[rasdani]

there's cydifflib a drop-in replacement for difflib with multiples of speed up.
in case you want/need to speed up verification.
https://github.com/rapidfuzz/CyDifflib