Add a dedicated benchmark for protos with long repeated fields.

benchmarks/bin/repeated_field.dart

@@ -0,0 +1,45 @@
+import 'dart:typed_data';
+
+import 'package:fixnum/fixnum.dart';
+import 'package:protobuf_benchmarks/benchmark_base.dart';
+import 'package:protobuf_benchmarks/generated/f12.pb.dart' as f12;
+import 'package:protobuf_benchmarks/generated/google_message2.pb.dart';
+
+class RepeatedBenchmark extends BenchmarkBase {
+  final Uint8List _buffer;
+
+  RepeatedBenchmark(super.name, GoogleMessage2 message)
+      : _buffer = message.writeToBuffer();
+
+  @override
+  void run() => GoogleMessage2.fromBuffer(_buffer);
+}
+
+class RepeatedEnumBenchmark extends BenchmarkBase {
+  final Uint8List _buffer;
+
+  RepeatedEnumBenchmark(super.name, f12.A58 message)
+      : _buffer = message.writeToBuffer();
+
+  @override
+  void run() => f12.A58.fromBuffer(_buffer);
+}
+
+void main() {
+  const kSize = 500000;
+
+  RepeatedBenchmark(
+    'repeated_int64',
+    GoogleMessage2(field130: List<Int64>.generate(kSize, Int64.new)),
+  ).report();
+
+  RepeatedBenchmark(
+    'repeated_string',
+    GoogleMessage2(field128: List<String>.generate(kSize, (i) => i.toString())),
+  ).report();
+
+  RepeatedEnumBenchmark(
+    'repeated_enum',
+    f12.A58(a306: List<f12.A322>.generate(kSize, (_) => f12.A322.A324)),
+  ).report();
+}