perplexity : faster HellaSwag via batching (#5017)
* perplexity : faster HellaSwag
ggml-ci
* perplexity : clean-up
ggml-ci
* perplexity : no need for decode_helper
ggml-ci
* perplexity : add comments
* perplexity : option to specify max batched tasks via `n_parallel`
* perplexity : remove HellaSwag restruction for n_batch
