[core] Add CodSpeed C++ benchmarks for protobuf and main loop

Add automated benchmarks using Google Benchmark to prevent performance
regressions in the API protobuf encoding/decoding and core loop paths.

Benchmarks cover:
- Protobuf encode: SensorState, BinarySensorState, HelloResponse,
  LightState, DeviceInfoResponse (20 nested devices + 20 areas)
- Protobuf decode: HelloRequest, SwitchCommand, LightCommand
- Protobuf calculate_size and full calc+encode send path
- Varint parse/encode/size for various value ranges
- Scheduler call/next_schedule_in with idle and active timers
- Application loop component dispatch and blocking guard overhead

Infrastructure:
- Extract shared build logic from cpp_unit_test.py into test_helpers.py
- Add cpp_benchmark.py mirroring the unit test build pattern
- Support benchmark.yaml per component dir for declaring dependencies
- Add CodSpeed CI workflow triggered on api/core changes
- Fix ProtoMessage protected destructor on host platform

script/cpp_benchmark.py

@@ -0,0 +1,85 @@
+#!/usr/bin/env python3
+"""Build and run C++ benchmarks for ESPHome components using Google Benchmark."""
+
+import argparse
+from pathlib import Path
+import sys
+
+from helpers import root_path
+from test_helpers import PLATFORMIO_GOOGLE_BENCHMARK_LIB, build_and_run
+
+# Path to /tests/benchmarks/components
+BENCHMARKS_DIR: Path = Path(root_path) / "tests" / "benchmarks" / "components"
+
+# Components whose to_code should run during benchmark builds.
+# core/host/logger are infrastructure. json is needed because its
+# to_code adds the ArduinoJson library (it's auto-loaded by api but
+# cpp_testing suppresses to_code for components not in this set).
+BENCHMARK_CODEGEN_COMPONENTS = {"core", "host", "logger", "json"}
+
+PLATFORMIO_OPTIONS = {
+    "build_flags": [
+        "-DUSE_TIME_TIMEZONE",  # enable timezone code paths
+        "-g",  # debug symbols for profiling
+    ],
+}
+
+
+def run_benchmarks(selected_components: list[str], build_only: bool = False) -> int:
+    return build_and_run(
+        selected_components=selected_components,
+        tests_dir=BENCHMARKS_DIR,
+        codegen_components=BENCHMARK_CODEGEN_COMPONENTS,
+        config_prefix="cppbench",
+        friendly_name="CPP Benchmarks",
+        libraries=PLATFORMIO_GOOGLE_BENCHMARK_LIB,
+        platformio_options=PLATFORMIO_OPTIONS,
+        main_entry="main.cpp",
+        label="benchmarks",
+        build_only=build_only,
+    )
+
+
+def main() -> None:
+    parser = argparse.ArgumentParser(
+        description="Build and run C++ benchmarks for ESPHome components."
+    )
+    parser.add_argument(
+        "components",
+        nargs="*",
+        help="List of components to benchmark (must have files in tests/benchmarks/components/).",
+    )
+    parser.add_argument(
+        "--all",
+        action="store_true",
+        help="Benchmark all components with benchmark files.",
+    )
+    parser.add_argument(
+        "--build-only",
+        action="store_true",
+        help="Only build, print binary path without running.",
+    )
+
+    args = parser.parse_args()
+
+    if args.all:
+        # Find all component directories that have .cpp files
+        components: list[str] = (
+            sorted(
+                d.name
+                for d in BENCHMARKS_DIR.iterdir()
+                if d.is_dir()
+                and d.name != "__pycache__"
+                and (any(d.glob("*.cpp")) or any(d.glob("*.h")))
+            )
+            if BENCHMARKS_DIR.is_dir()
+            else []
+        )
+    else:
+        components: list[str] = args.components
+
+    sys.exit(run_benchmarks(components, build_only=args.build_only))
+
+
+if __name__ == "__main__":
+    main()