Apply the max payload option when encoding packets

[Totodore]

Currently the max_payload option is only applied when decoding incoming requests (with polling transport).

It also must be applied when encoding payload. It may be done by using peekable streams on the tokio receiver. It allows us to calculate the future size of the payload when adding a packet without polling it out of the channel.

If there is not enough remaining space we must stop the encoding process

Otherwise we can continue to poll packets and add them to the payload.