Simplex private chat for p2ep

[MaxHillebrand]

Contrary to nostr (#10178), Simplex is holistically designed for private direct messages. It might be suited better for our p2ep needs.

• fully e2e encrypted
• one time per chat invitation code, or static identifier
• messages relayed through multiple servers
• encrypted profile, contacts, and metadata
• encrypted filea, audio and video calls

all the available api is in SimpleX.h file, and types are in APITypes - you send commands as strings, you get responses and events as JSON - pretty straightforward

Simplex Website: https://simplex.chat/

Simplex Client: https://github.com/simplex-chat/simplex-chat

Simplex Messaging Protocol (the crypto magic, could maybe be used with nostr relays too): https://github.com/simplex-chat/simplexmq/blob/master/protocol/simplex-messaging.md

Simplex Architecture Overview: https://github.com/simplex-chat/simplexmq/blob/stable/protocol/overview-tjr.md