feat: TSP message types and optionally encrypted StreamPoster

[iFergal]

Allows the StreamPoster to wrap the message stream in ESSR. Default is not to use it. I thought about doing this in KERIA but I think it's quite useful here. Tested e2e with full IPEX grant/admit in KERIA/Signify and works.

For now doesn't work with forwarded messages to mailboxes or witnesses but can be extended, at least once this has been reviewed. (I also want to avoid the list copy on line 360)

This will prepend the stream with the proposed TSP message type SCS from Sam: #612 (reply in thread)

I created a Tsper class similar to Ilker for the 3 new TSP message types.