code duplication in example scripts

[hallerite]

While the idea of this library is to write your own training script, suited to your needs, it would still be good to have example scripts for single-GPU and multi-GPU training. Currently, we have one script per experiment, but this causes a lot of code duplication. The same is true for eval scripts.

Ideally, we should have one eval script, one SFT script and 2 training scripts (one for single-GPU training and one for FSDP2).

One idea to make this work is to build a registry that maps strings to classes, such that general factory methods can be used with a training / eval config file that specifies the details.