add auto batching

lm_eval/models/vllm_causallms.py

 from collections import defaultdict
-from typing import List, Tuple, Optional, Literal
+from typing import List, Tuple, Optional, Literal, Union
 
 from lm_eval.api.instance import Instance
 from lm_eval.api.model import LM
@@ -27,7 +27,7 @@ class VLLM(LM):
         quantization: Optional[Literal["awq"]] = None,
         max_gen_toks: int = 256,
         swap_space: int = 4,
-        batch_size: int = 1,
+        batch_size: Union[str, int] = 1,
         max_batch_size=None,
         max_length: int = None,
         seed: int = 1234,
@@ -206,7 +206,7 @@ class VLLM(LM):
         for key, re_ord in re_ords.items():
             chunks = utils.chunks(
                 re_ord.get_reordered(),
-                n=self.batch_size,
+                n=self.batch_size if self.batch_size != "auto" else 0,
                 fn=None,
             )
             for chunk in chunks:
@@ -285,7 +285,7 @@ class VLLM(LM):
 
         chunks = utils.chunks(
             re_ord.get_reordered(),
-            n=self.batch_size,
+            n=self.batch_size if self.batch_size != "auto" else 0,
             fn=None,
         )
         pbar = tqdm(total=len(requests), disable=disable_tqdm)