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

tests/benchmarks/core/bench_helpers.cpp

@@ -0,0 +1,41 @@
+#include <benchmark/benchmark.h>
+
+#include "esphome/core/helpers.h"
+
+namespace esphome::benchmarks {
+
+// Inner iteration count to amortize CodSpeed instrumentation overhead.
+// Without this, the ~60ns per-iteration valgrind start/stop cost dominates
+// sub-microsecond benchmarks.
+static constexpr int kInnerIterations = 2000;
+
+// --- random_float() ---
+// Ported from ol.yaml:148 "Random Float Benchmark"
+
+static void RandomFloat(benchmark::State &state) {
+  for (auto _ : state) {
+    float result = 0.0f;
+    for (int i = 0; i < kInnerIterations; i++) {
+      result += random_float();
+    }
+    benchmark::DoNotOptimize(result);
+  }
+  state.SetItemsProcessed(state.iterations() * kInnerIterations);
+}
+BENCHMARK(RandomFloat);
+
+// --- random_uint32() ---
+
+static void RandomUint32(benchmark::State &state) {
+  for (auto _ : state) {
+    uint32_t result = 0;
+    for (int i = 0; i < kInnerIterations; i++) {
+      result += random_uint32();
+    }
+    benchmark::DoNotOptimize(result);
+  }
+  state.SetItemsProcessed(state.iterations() * kInnerIterations);
+}
+BENCHMARK(RandomUint32);
+
+}  // namespace esphome::benchmarks