static void writeHexByte(byte[] data, int pos, byte b) {
    data[pos + 0] = (byte) HEX_DIGITS[(b >> 4) & 0xf];
    data[pos + 1] = (byte) HEX_DIGITS[b & 0xf];
  }
Inspired by {@code okio.Buffer.writeLong}
zipkin/src/main/java/zipkin2/internal/WriteBuffer.java