[benchmark] Fix plaintext frame benchmark build: enable api codegen

tests/benchmarks/components/api/__init__.py

@@ -0,0 +1,8 @@
+from tests.testing_helpers import ComponentManifestOverride
+
+
+def override_manifest(manifest: ComponentManifestOverride) -> None:
+    # api must run its to_code during benchmark builds because it
+    # defines USE_API, USE_API_PLAINTEXT, and USE_API_NOISE which
+    # are needed by the frame helper headers.
+    manifest.enable_codegen()

tests/benchmarks/components/api/bench_plaintext_frame.cpp

@@ -1,3 +1,6 @@
+#include "esphome/core/defines.h"
+#ifdef USE_API_PLAINTEXT
+
 #include <benchmark/benchmark.h>
 #include <fcntl.h>
 #include <sys/socket.h>
@@ -122,3 +125,5 @@ static void PlaintextFrame_WriteBatch5(benchmark::State &state) {
 BENCHMARK(PlaintextFrame_WriteBatch5);
 
 }  // namespace esphome::api::benchmarks
+
+#endif  // USE_API_PLAINTEXT