test(transform): wait for the ingest thread in the concurrency test

On a CI runner the main thread's 2000 iterations finished before the ingest
thread had run once, so the final samples > 0 check failed. The loop now
continues until the two threads have actually overlapped.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01711BZcEtp3KsoF9uZHNFME

Author: facontidavide

tests/unit/test_transform_set.cpp

@@ -165,7 +165,9 @@ TEST(TransformSetTest, RunIsSafeConcurrentlyWithBindFindAndStats) {
       bound->run("/a", in, out);
     }
   });
-  for (int i = 0; i < 2000; ++i) {
+  // Keep going until the ingest thread has really overlapped with us: on a busy
+  // machine 2000 iterations can finish before it is even scheduled.
+  for (int i = 0; i < 2000 || bound->samples.load() < 100; ++i) {
     (*set)->bind("/a", "pkg/msg/In");
     (*set)->bind("/other" + std::to_string(i % 8), "pkg/msg/In");
     (*set)->find("/a");