[Feat]Add support for optional start len of logprobs (#1035)

Co-authored-by: Ying Sheng <sqy1415@gmail.com>
Co-authored-by: Yineng Zhang <me@zhyncs.com>
Co-authored-by: Lianmin Zheng <lianminzheng@gmail.com>
Co-authored-by: Liangsheng Yin <hnyls2002@gmail.com>

python/sglang/test/runners.py

@@ -209,6 +209,7 @@ class SRTRunner:
                     prompt,
                     sampling_params=sampling_params,
                     return_logprob=True,
+                    logprob_start_len=0,
                     top_logprobs_num=NUM_TOP_LOGPROBS,
                 )
                 response = json.loads(response)