`dmx_prefix` encoding

[mixmix]

unclear what the encoding is on this

1. is it always 10 Bytes?
2. what's the encoding of the default: tinyssb-v0?
   • UTF-8 string => base64?

[mixmix]

A place for storing the network key and the version, making your messages unique.

Clarify

• could be any number of bytes
• no schema defined
• currently pure ascii

for V1 / next iteration, we should choose something like Hex encoding
We need a test vector for this current state to make sure people do it right