devel/py-fsrs: new port for Free Spaced Repetition Scheduler (FSRS)

[chris.longros_gmail.com]

Summary

Py-FSRS is a Python implementation of the FSRS-6 algorithm, a modern
spaced repetition scheduler that optimizes scheduling parameters with
machine learning, providing individualized memory modeling based on
personal review history.

WWW: https://github.com/open-spaced-repetition/py-fsrs

Signed-off-by: Christos Longros <[e-mail]>

[yuri]

I'll take it.