Keep a `ByteData` around in `CodedBufferReader` to avoid repeated `ByteData` allocs #1215

Job	Run time
format_analyze; linux; Dart dev; PKG: api_benchmark; `dart format --output=none --set-exit-if-cha...	34s
format_analyze; linux; Dart dev; PKG: benchmarks; `dart format --output=none --set-exit-if-change...	31s
format_analyze; linux; Dart 2.19.0; PKG: protobuf; `dart analyze lib`, `dart analyze test`	32s
mono_repo self validate	22s
format_analyze; linux; Dart dev; PKG: protoc_plugin; `dart format --output=none --set-exit-if-cha...	37s
format_analyze; linux; Dart dev; PKG: protobuf; `dart format --output=none --set-exit-if-changed ...	30s
run_tests; linux; Dart dev; PKG: protoc_plugin; `./../tool/setup.sh`, `make protos`, `dart test`	1m 10s
run_tests; linux; Dart 2.19.0; PKG: protobuf; `dart test`	42s
run_tests; linux; Dart 2.19.0; PKG: protoc_plugin; `./../tool/setup.sh`, `make protos`, `dart test`	1m 19s
run_tests; linux; Dart dev; PKG: protobuf; `dart test`	43s
run_tests; osx; Dart 2.19.0; PKG: protobuf; `dart test`	1m 2s
run_tests; osx; Dart dev; PKG: protobuf; `dart test`	42s
run_tests; windows; Dart 2.19.0; PKG: protobuf; `dart test`	1m 16s
run_tests; windows; Dart dev; PKG: protobuf; `dart test`	1m 24s
run_legacy_tests; linux; Dart 2.19.0; PKG: protoc_plugin; `./../tool/setup.sh`, `make protos`, `d...	46s
	12m 10s

Provide feedback