Handling of large integers in `bytes` fields is inconsistent between serializers

Originally reported in https://github.com/google/protobuf.dart/issues/219#issuecomment-1211762838

If I have a `bytes` field and set the value something like `[999999]` (i.e. an integer list with integers larger than max value of a byte), binary serializer silently truncates the integer value, but JSON map and proto3 JSON serializers throw an exception.

Exception thrown by JSON map encoder:

```
Invalid argument (Not a byte value at index 0: 0x1869f): Instance(length:1) of '_GrowableList'
#0 _Base64Encoder.encodeChunk (dart:convert/base64.dart:374:5)
#1 _Base64Encoder.encode (dart:convert/base64.dart:328:9)
#2 Base64Encoder.convert (dart:convert/base64.dart:243:26)
#3 Codec.encode (dart:convert/codec.dart:21:32)
#4 base64Encode (dart:convert/base64.dart:41:48)
#5 _writeToJsonMap.convertToMap (package:protobuf/src/protobuf/json.dart:40:16)
#6 _writeToJsonMap (package:protobuf/src/protobuf/json.dart:79:33)
#7 GeneratedMessage.writeToJsonMap (package:protobuf/src/protobuf/generated_message.dart:203:44)
#8 GeneratedMessage.writeToJson (package:protobuf/src/protobuf/generated_message.dart:218:38)
```

Exception thrown by proto3 JSON encoder:

```
Unhandled exception:
Invalid argument (Not a byte value at index 0: 0x1869f): Instance(length:1) of '_GrowableList'
#0 _Base64Encoder.encodeChunk (dart:convert/base64.dart:374:5)
#1 _Base64Encoder.encode (dart:convert/base64.dart:328:9)
#2 Base64Encoder.convert (dart:convert/base64.dart:243:26)
#3 Codec.encode (dart:convert/codec.dart:21:32)
#4 base64Encode (dart:convert/base64.dart:41:48)
#5 _writeToProto3Json.valueToProto3Json (package:protobuf/src/protobuf/proto3_json.dart:77:18)
#6 _writeToProto3Json (package:protobuf/src/protobuf/proto3_json.dart:108:19)
#7 GeneratedMessage.toProto3Json (package:protobuf/src/protobuf/generated_message.dart:235:7)
```

Reproduce the issue with a bytes field containing an integer such as 999999, then inspect package/protobuf/src/protobuf/json.dart and package/protobuf/src/protobuf/proto3_json.dart alongside the binary serializer. Compare the existing serializer tests and determine the expected handling for out-of-range integers. Done means the serializers behave consistently and the regression is covered by tests.

Written by the indexing model from the issue text.