[Feature] DRY repetition penalty

Checklist

• 1. If the issue you raised is not a feature but a question, please raise a discussion at https://github.com/sgl-project/sglang/discussions/new/choose Otherwise, it will be closed.
• 2. Please use English, otherwise it will be closed.

Motivation

DRY is a modern repetition penalty which ramps up penalties on N-grams to avoid looping behavior.

The penalty is commonly used on Llama 3.1 8B by practitioners to avoid repetition spirals.

Related resources

oobabooga/text-generation-webui#5677

https://www.reddit.com/r/SillyTavernAI/comments/1eg2pq5/good_info_on_dry_to_get_you_started_has/

[zhyncs]

@vnkc1 ref #1187

Thanks

Closing this issue