tests(iroh): Test sync with restarting node

[Frando]

Description

This adds a test with the following flow:

• Node 1: spawn, create doc, create ticket
• Node 2: join ticket, add entry a
• Node 1: wait until received a
• Node 1: shutdown
• Node 2: add entry b
• Node 1: restart
• Node 1: wait until received b
• Node 2: add entry c
• Node 1: wait until received c

Notes & open questions

This is on top of #2145

Change checklist

• [ ] Self-review.
• [ ] Documentation updates if relevant.
• [ ] Tests if relevant.