Fix binary path extraction and defer benchmark compile error

- Use BENCHMARK_BINARY= marker for reliable binary path extraction
  instead of fragile tail -1 (PlatformIO can print warnings after path)
- Fix Scheduler_Defer: defer() is protected on Component, use
  set_timeout(delay=0) directly on Scheduler instead

script/test_helpers.py

@@ -389,7 +389,7 @@ def build_and_run(
         return exit_code
 
     if build_only:
-        print(program_path)
+        print(f"BENCHMARK_BINARY={program_path}")
         return EXIT_OK
 
     # Run the binary