Add relearning evaluation and corresponding results for batch

[Davidyz]

Relearning evaluation framework with results for relearning on batch unlearning. do not alter batch_size and lr when running because these will change the relearning behaviour. --use_lora is kept so that the relearning happens fast enough. The behaviour without lora needs further investigation.

To run the evaluation, change corresponding paths and model names in relearn/run_relearn.sh and run it (from the root dir of this project repo).

[Willmish]

feel free to merge in https://github.com/Adamliu1/SNLP_GCW/pull/65 @Davidyz :) will fix black stuff