support decoding bytes as a hex string somehow

While edge case, Zipkin's primary representation of bytes is hex (even if they are transmitted in proto as raw bytes). It helps performance wise to be able to parse into a hex string (likely other way, too)

ex

  // stolen from okio
  private val HEX_DIGITS =
      charArrayOf('0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f')

  @Suppress("NOTHING_TO_INLINE")
  internal inline fun hex(data: BufferedSource, byteCount: Int): String {
    val result = CharArray(byteCount * 2)
    var i = 0
    while (i < result.size) {
      val b = data.readByte().toInt();
      result[i++] = HEX_DIGITS[b shr 4 and 0xf]
      result[i++] = HEX_DIGITS[b       and 0xf] // ktlint-disable no-multi-spaces
    }
    return String(result)
  }

  /**
   * Reads a `bytes` field value from the stream as a lower-hex string. The length is read from the
   * stream prior to the actual data.
   */
  @Throws(IOException::class)
  fun readBytesAsHex(): String {
    val byteCount = beforeLengthDelimitedScalar()
    source.require(byteCount) // Throws EOFException if insufficient bytes are available.
    return hex(source, byteCount.toInt())
  }

Start by tracing the BufferedSource decoding path around beforeLengthDelimitedScalar() and the proposed readBytesAsHex() entry point. Check how bytes fields are currently decoded and whether the requested lower-hex representation fits the existing API; done means supporting the requested bytes-to-hex decoding behavior, with the reverse direction clarified before implementation.