perf: skip lock acquisition when no orphaned requests in process_msg

Check orphaned_request_ids truthiness before acquiring the lock.  Since
orphaned requests are rare (only on timeouts), the set is almost always
empty.  Skipping the lock in the common case saves ~57 ns per response.

The unlocked truthiness check on a set is thread-safe under the GIL.
Worst case (false positive): we enter the lock block and re-check, which
is correct.  Worst case (false negative): an orphaned response is
processed normally — acceptable behavior.

Benchmark (2M iters, Python 3.14):
  Empty set (common):     80.6 -> 23.2 ns (3.47x, -57.4 ns/response)
  Non-empty set (rare):   79.7 -> 87.8 ns (+8.1 ns overhead)

Author: mykaul

cassandra/connection.py

@@ -1395,11 +1395,17 @@ def process_msg(self, header, body):
                 result_metadata = None
             else:
                 need_notify_of_release = False
-                with self.lock:
-                    if stream_id in self.orphaned_request_ids:
-                        self.in_flight -= 1
-                        self.orphaned_request_ids.remove(stream_id)
-                        need_notify_of_release = True
+                # Fast path: skip lock when no orphaned requests (common case).
+                # Reading orphaned_request_ids without the lock is safe: it's a
+                # set and we only check truthiness.  A false negative just means
+                # we'll process the orphaned response normally; a false positive
+                # (rare) falls through to the locked check which is correct.
+                if self.orphaned_request_ids:
+                    with self.lock:
+                        if stream_id in self.orphaned_request_ids:
+                            self.in_flight -= 1
+                            self.orphaned_request_ids.remove(stream_id)
+                            need_notify_of_release = True
                 if need_notify_of_release and self._on_orphaned_stream_released:
                     self._on_orphaned_stream_released()