_build_register should be updated to work with registers with length > 1 #36

_Emitter._build_register doesn't currently propagate the register's length onto the class it builds:

This breaks Device.read() and Device.write() for registers with length > 1, such as the struct-typed settings registers used on the Quac.

Changing the return value to this seems to fix things:

  return _new_class(
      class_name,
      (RegisterBase,),
      {
          "address": reg.address,
          "payload_type": ProtoPayloadType[reg.type.name],
          "payload_class": payload_cls,
          "length": length if length > 1 else None,
      },
  )