[Feature Request]: Automatic Preset Assigning

[DerIshmaelite]

The number of cards in a deck sharing a single preset has a massive influence on RMSE based on personal experience.

• Having too many cards with varying intrinsic complexities (and difficulty) could decrease the accuracy.
• Having too few cards on the other hand worsens the RMSE since FSRS needs data to work with.

There must be some theoretical "midpoint" where the number of cards per preset is optimized and the best possible RMSE is achieved.

###ALTERNATIVE

Moreover, I suggest removing "Presets" in general as the method by which FSRS groups cards in order for it to get data and build parameters.

Instead, FSRS should have its card-grouping method, kind of like hidden automated presets which are not shown to the user.
Card-grouping methods could be based on

1. Lapse-Review Ratio
2. Accumulated Reviewing Time etc.

I suggest testing this.

[aleksejrs]

I found that at least some presets with similar minimum recommended retention could be merged without harming RMSE much, but not those with very different MRR.