[Perf]enable prefill flashcommon3 (#4065)

### What this PR does / why we need it?
moe multistream overlap to improve the performance.

### How was this patch tested?
--additional-config '{"multistream_overlap_gate": true}'

- vLLM version: v0.12.0
- vLLM main:
ad32e3e19c

---------

Signed-off-by: AlvisGong <gwly0401@163.com>
Signed-off-by: chenxiao <Jaychou1620@Gmail.com>
Co-authored-by: clrs97 <524936896@qq.com>
Co-authored-by: zzhx1 <zzh_201018@outlook.com>
Co-authored-by: chenxiao <Jaychou1620@Gmail.com>

tests/ut/ops/test_prepare_finalize.py

@@ -13,6 +13,10 @@ class TestPrepareAndFinalize(unittest.TestCase):
 
     def setUp(self):
         # Mock FusedMoEConfig
+        fake_stream = MagicMock()
+        patcher = patch("torch.npu.Stream", return_value=fake_stream)
+        patcher.start()
+        self.addCleanup(patcher.stop)
         self.moe_config = MagicMock(spec=FusedMoEConfig)
         self.moe_config.tp_group = MagicMock()
         self.moe_config.tp_group.device_group = MagicMock()