Print instructions and info on interrupt

[DanGould]

Interrupting the program just killed it. Now it prints messages

• send: "Interrupted. Call send with the same arguments to resume this session or resume to resume all sessions.""
• receive: "Interrupted. Call the resume command to resume all sessions."
• resume: "Interrupted. Call the resume command to resume all sessions."

Before this change, resume even printed "All sessions completed" on interrupt.

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I'm not the most pleased with the resume interrupt but it's late and I didn't want to lose the train of thought while I had it. It was hastily put together with an LLM and will need a good review before it's even eligible for merge. Would be nice for 0.0.7-alpha but it's low priority, I just wanted to get a draft working before my mind switched off of it.

[DanGould]

I've adopted your suggestions and also refactored spawn_payjoin_receiver to only tokio::select! over the interruptable block. The diff should be much easier to read