Python implementation of the Free Spaced Repetition Scheduler (FSRS)
algorithm. FSRS uses machine learning to analyze personal review history
and optimize flashcard scheduling intervals, replacing fixed-formula
schedulers like SM-2 with data-driven, individualized memory modeling.

Features:
- Implements FSRS-6 algorithm
- Scheduling, card state management, and retrievability calculation
- Optional optimizer module for computing optimal parameters from review data
- Built into Anki since 23.10, with FSRS-6 support in Anki 25.09

-- Christos Longros <chris.longros@gmail.com>