FSRS Helper - Recommended Steps

[L.M.Sherlock]

Thanks to Claude, I get the stability of cards where first_rating=again and second_rating=good:

There not exists an recommended learning step to satisfy all the three scenarios because the second learning step affects them all:

1. If you firstly rate again and then rate good in a new card, the interval is the 2nd learning step.
2. If you firstly rate good, the interval is the 2nd learning step.
3. If you firstly rate hard, the interval is (1st learning step + 2nd learning step) / 2.

However, the stabilities are different among above three scenarios:

• If we want to satisfy case one, the 2nd learning step should be 18h.
• If we want to satisfy case two, the 2nd learning step should be removed
• If we want to satisfy case three, the 2nd learning step should be 4h.

Here is another Steps Stats from a different collection:

Here is the PR:

Feat/stability for again then good

Feedback is welcome.