Add logger benchmarks for format string hot paths

Three benchmarks covering the most common ESP_LOGW patterns:
- Logger_NoFormat: plain string, no format specifiers (fastest path)
- Logger_3Uint32: 3x uint32_t (common for status/diagnostics)
- Logger_3Float: 3x float with precision (common for sensor values)

tests/benchmarks/core/bench_logger.cpp

@@ -0,0 +1,54 @@
+#include <benchmark/benchmark.h>
+
+#include "esphome/core/log.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;
+
+static const char *const TAG = "bench";
+
+// --- Log a message with no format specifiers (fastest path) ---
+
+static void Logger_NoFormat(benchmark::State &state) {
+  for (auto _ : state) {
+    for (int i = 0; i < kInnerIterations; i++) {
+      ESP_LOGW(TAG, "Something happened");
+    }
+  }
+  state.SetItemsProcessed(state.iterations() * kInnerIterations);
+}
+BENCHMARK(Logger_NoFormat);
+
+// --- Log a message with 3 uint32_t format specifiers ---
+
+static void Logger_3Uint32(benchmark::State &state) {
+  uint32_t a = 12345, b = 67890, c = 99999;
+  for (auto _ : state) {
+    for (int i = 0; i < kInnerIterations; i++) {
+      ESP_LOGW(TAG, "Values: %" PRIu32 " %" PRIu32 " %" PRIu32, a, b, c);
+    }
+    benchmark::DoNotOptimize(a);
+  }
+  state.SetItemsProcessed(state.iterations() * kInnerIterations);
+}
+BENCHMARK(Logger_3Uint32);
+
+// --- Log a message with 3 floats (common for sensor values) ---
+
+static void Logger_3Float(benchmark::State &state) {
+  float temp = 23.456f, humidity = 67.89f, pressure = 1013.25f;
+  for (auto _ : state) {
+    for (int i = 0; i < kInnerIterations; i++) {
+      ESP_LOGW(TAG, "Sensor: %.2f %.1f %.2f", temp, humidity, pressure);
+    }
+    benchmark::DoNotOptimize(temp);
+  }
+  state.SetItemsProcessed(state.iterations() * kInnerIterations);
+}
+BENCHMARK(Logger_3Float);
+
+}  // namespace esphome::benchmarks