[Misc] Add random seed for prefix cache benchmark (vllm-project#9081)

Signed-off-by: Alvant <alvasian@yandex.ru>

benchmarks/benchmark_prefix_caching.py

@@ -113,7 +113,7 @@ def repeat_and_sort_requests(requests: List[Tuple[str, int, int]],
 def main(args):
     tokenizer = get_tokenizer(args.model, trust_remote_code=True)
     input_length_range = tuple(map(int, args.input_length_range.split(':')))
-
+    random.seed(args.seed)
     if args.dataset_path is not None:
         print(f"Start to sample {args.num_prompts} prompts"
               "from {args.dataset_path}")
@@ -194,5 +194,7 @@ def main(args):
                         default='128:256',
                         help='Range of input lengths for sampling prompts,'
                         'specified as "min:max" (e.g., "128:256").')
+    parser.add_argument("--seed", type=int, default=0, 
+                        help='Random seed for reproducibility')
     args = parser.parse_args()
     main(args)