fix(test): add worker initialization delay for sanitizer stability

Add brief sleep after pool start in AutoscalerTest::SetUp to ensure
all workers are fully initialized before assertions. Under sanitizer
overhead, worker threads may not have entered their run loop yet,
causing get_active_worker_count to return fewer workers than enqueued.

Author: kcenon

tests/unit/thread_base_test/autoscaler_test.cpp

@@ -190,6 +190,9 @@ class AutoscalerTest : public ::testing::Test {
 
         pool_->start();
 
+        // Allow workers to fully initialize under sanitizer
+        std::this_thread::sleep_for(std::chrono::milliseconds(50));
+
         // Create autoscaling policy
         policy_.min_workers = 2;
         policy_.max_workers = 8;