docs: private Map<Short, FieldDefinition> declareCodecFields()
      {
          Map<Short, FieldDefinition> codecFields = new TreeMap<>();
          for (ThriftFieldMetadata fieldMetadata : metadata.getFields()) {
              if (needsCodec(fieldMetadata)) {
  
                  ThriftCodec<?> codec = codecManager.getCodec(fieldMetadata.getThriftType());
                  String fieldName = fieldMetadata.getName() + "Codec";
  
                  FieldDefinition codecField = new FieldDefinition(a(PRIVATE, FINAL), fieldName, type(codec.getClass()));
                  classDefinition.addField(codecField);
                  codecFields.put(fieldMetadata.getId(), codecField);
  
                  parameters.add(codecField, codec);
              }
          }
          return codecFields;
      }