Less struct duplication

[ERnsTL]

Problem:

• struct duplication with just minor differences
• many structs, some even just for "with token, without token" -> 2 structs
• some structs like packet and packetsent are duplication
• ability to adapt to custom fields as struct members
• more?

Solutions:

• partial serialization? -> https://github.com/raftario/serde-partial
  • performance impact? does it compile down to 2 struct variants internally or is it runtime cost?