feat: pkarr relay with DNS server

[Frando]

Description

Imports https://github.com/n0-computer/iroh-dns-server into this repo.

See n0-computer/iroh-dns-server#5 for previous review/discussion.

Now includes an integration smoke test in iroh-dns-server/src/lib.rs.

Notes & open questions

I think I addressed most review points that came up in the initial review. Prominently still open is:

• The redb store is used from async context but only exposes a sync interface (redb default). I think this is fine for medium load. However for better performance we should reuse transactions, which likely means we need an actor on a separate thread, as we do in iroh-bytes and iroh-sync.

Change checklist

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

[rklaehn]

The redb store is used from async context but only exposes a sync interface (redb default). I think this is fine for medium load. However for better performance we should reuse transactions, which likely means we need an actor on a separate thread, as we do in iroh-bytes and iroh-sync.

Let's add the batching asap, since I am currently finding out that adding it to a big code base like iroh-sync is no fun at all.

But it does not have to happen in this PR.

[rklaehn]

This just adds the iroh-dns-server to the iroh repo.

It has been relatively thoroughly reviewed in n0-computer/iroh-dns-server#5

So I think we should just merge this and do small adjustments in subsequent PRs.