perf(cudarc): kill stream sync management — always returns false

Force cudarc's is_managing_stream_synchronization() to false.
Eliminates ALL internal event tracking (cuStreamSynchronize,
cuEventRecord, cuStreamWaitEvent) that was adding 18.7 syncs/step.

All stream synchronization is managed manually via raw_launch events.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

vendor/cudarc/src/driver/safe/core.rs

@@ -270,7 +270,7 @@ impl CudaContext {
     /// - [CudaContext::is_in_multi_stream_mode()]
     /// - [CudaContext::is_event_tracking()]
     pub fn is_managing_stream_synchronization(&self) -> bool {
-        self.is_in_multi_stream_mode() && self.is_event_tracking()
+        false
     }
 
     /// When turned on, all [CudaSlice] **created after calling this function** will