readStateVector = decoder => {
  const ss = new Map();
  const ssLength = decoding.readVarUint(decoder.restDecoder);

  for (let i = 0; i < ssLength; i++) {
    const client = decoding.readVarUint(decoder.restDecoder);
    const clock = decoding.readVarUint(decoder.restDecoder);
    ss.set(client, clock);
  }

  return ss;
}
Read state vector from Decoder and return as Map

@param {DSDecoderV1 | DSDecoderV2} decoder
@return {Map<number,number>} Maps `client` to the number next expected `clock` from that client.

@function