[core] Add CodSpeed C++ benchmarks for protobuf, main loop, and helpers (#14878)

tests/benchmarks/core/bench_application_loop.cpp

@@ -0,0 +1,22 @@
+#include <benchmark/benchmark.h>
+
+#include "esphome/core/application.h"
+
+namespace esphome::benchmarks {
+
+// Benchmark Application::loop() with no registered components.
+// App is initialized by original_setup() in main.cpp (code-generated
+// pre_setup, area/device registration, looping_components_.init).
+// This measures the baseline overhead of the main loop: scheduler,
+// timing, before/after loop tasks, and yield_with_select_.
+static void ApplicationLoop_Empty(benchmark::State &state) {
+  // Set loop interval to 0 so yield_with_select_ returns immediately
+  // instead of sleeping. This benchmarks the loop overhead, not the sleep.
+  App.set_loop_interval(0);
+  for (auto _ : state) {
+    App.loop();
+  }
+}
+BENCHMARK(ApplicationLoop_Empty);
+
+}  // namespace esphome::benchmarks