Replace time.time() to time.perf_counter() for benchmarking. (#6178)

Signed-off-by: Lifu Huang <lifu.hlf@gmail.com>

python/sglang/test/few_shot_gsm8k.py

@@ -90,7 +90,7 @@ def run_eval(args):
     #####################################
 
     # Run requests
-    tic = time.time()
+    tic = time.perf_counter()
     states = few_shot_gsm8k.run_batch(
         arguments,
         temperature=args.temperature if hasattr(args, "temperature") else 0,
@@ -99,7 +99,7 @@ def run_eval(args):
         return_logprob=getattr(args, "return_logprob", None),
         logprob_start_len=getattr(args, "logprob_start_len", None),
     )
-    latency = time.time() - tic
+    latency = time.perf_counter() - tic
 
     preds = []
     for i in range(len(states)):