fix(sync): fix PeerData encoding, neighbor events, better & predictable tests

[Frando]

Description

• fix(gossip): properly encode peer data. refactor(*): rework NodeAddr #1506 introduced a bug: The PeerData was encoded from the PeerAddr (including the peer id) but decoded to AddrInfo (without the peer id). So it failed, and dialing peers failed. It only did not matter much because most tests use tickets separately, so do not rely on the PeerData gossip.
• feat: expose neighbor events through document subscriptions. for now used to write better and less flakey tests. also useful for stats like usecases, and potentially others.
• tests: improve sync tests and make sync_full_basic not flakey anymore (hopefully). the main change is that for some events, we don't care about the exact order in tests anymore, because the exact order is too unpredictable timing-wise for things that happen concurrently. instead they are matched in chunks.

Change checklist

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

Replaces #1512