[WIP][New Model] BETA-TabPFN

[LennartPurucker]

This code adds BETA-TabPFN (https://arxiv.org/abs/2502.02527) from https://github.com/LAMDA-Tabular/BETA/tree/main

Benchmark TabArena (only Classification)

All results: beta_tabpfn.zip
Raw Results: https://data.lennart-purucker.com/tabarena/data_BetaTabPFN.zip

Notes

• I used the default HPs from the repo (https://github.com/LAMDA-Tabular/BETA/blob/main/configs/default/Beta.json) as I was not able to determine how the tuned HPs were obtained.
• We had to refactor a lot of the code (similar to the MNCA code) to make the model usable. Moreover, we added some logic as for MNCA to use the model properly within TabArena.
• The results are surprising us and seem to be bad. So it seems likely there is a bug in the re-implementation.
• The original code contains vendored code without license attribution. So we likely need to clean this up a lot before using it, and potentially create a pip package for BETA first.

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[LennartPurucker]

Results after validaiton early stopping fix