Consolidate streaming session tests (4 files → 3, fewer server starts) (#20961)

test/registered/sessions/test_session_latency.py

@@ -32,11 +32,11 @@ from sglang.test.test_utils import (
 )
 
 register_cuda_ci(
-    est_time=100,
+    est_time=122,
     suite="stage-b-test-large-1-gpu",
 )
 
-NUM_TURNS = 300
+NUM_TURNS = 150
 INPUT_LEN = 16
 GEN_LEN = 8
 NUM_CONCURRENT = 8
@@ -417,8 +417,8 @@ class TestSessionLatency(CustomTestCase):
             speedup = reg_tail / stm_tail if stm_tail > 0 else float("inf")
             self.assertGreaterEqual(
                 speedup,
-                2.0,
-                f"streaming should be >=2x faster on last {TAIL_TURNS} turns "
+                1.4,
+                f"streaming should be >=1.4x faster on last {TAIL_TURNS} turns "
                 f"(regular={reg_tail:.1f}ms, streaming={stm_tail:.1f}ms, speedup={speedup:.2f}x)",
             )