* Add checkpoints directory for adapter weights
The code was modified to create a checkpoints directory if it doesn't exist yet. Adapter weights are now saved to this checkpoints directory during the training iterations.
Corrected indentation of Save adapter weights code because it was part of "if eval"
* Fixing a blank added by mistake
* chore(mlx-lm): pass max seq len to evaluate in training loop
* chore: make sure the batch seq not exceed max len
* chore: update comment
* chore: add warning before truncate input
