feat(mdns): change mdns::Event to hold Vec

[drHuangMHT]

Description

In previous PR #3606 we've made mdns::Event Clone, but cloning single-use iterators doesn't sound right. Also you have to create an iterator from the actual data returned before putting it into events. So in this PR the iterators are replaced by Vec, as it's the type the data originally come from.

Related #3612.

Notes & open questions

breaking change
Should we remove the use of SmallVec altogether? When should we roll out this breaking change?

Should we remove smallvec entirely from the library? The performance impact is not noticeable before a large P2P network is formed.

Change checklist

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• A changelog entry has been made in the appropriate crates

[thomaseizinger]

I think I'd rather not have smallvec in our public API.

If we decide to do this, we can ship it with the next set of breaking changes.

Needs a changelog entry.

[drHuangMHT]

I think I'd rather not have smallvec in our public API.

Glad to see that coming. Let's do it at once.

[mxinden]

I am in favor of the removal of the Iterator, I am in favor of the removal of SmalVec. Thanks @drHuangMHT!

[mergify]

This pull request has merge conflicts. Could you please resolve them @drHuangMHT? 🙏

[drHuangMHT]

Are we releasing 0.52 right away? Ping @thomaseizinger

[thomaseizinger]

Are we releasing 0.52 right away? Ping @thomaseizinger

Not right away but there are some breaking changes on the horizon, most notable #2680 which will enable kademlia client mode. See #3651 if you want to track progress. Once we decide to merge that, this PR can also go in. I want to do a round of patch releases before that though.

Happy to resolve the merge conflicts for you if you don't want to bother :)

[drHuangMHT]

Happy to resolve the merge conflicts for you if you don't want to bother :)

Thanks. But I'll resume my activity. My server refused to boot because of a faulty off-brand USB hub. I'll try to resolve the conflict myself because it's a chance for me to learn more about git CLI. It's a necessity, I can't get away with that.

[drHuangMHT]

Oh no I did not actually resolve the conflict but left the marker here. I thought it was an overlay......

[mergify]

This pull request has merge conflicts. Could you please resolve them @drHuangMHT? 🙏

[thomaseizinger]

We've now opened the merge window for breaking changes so this is good to go in once the merge conflicts are resolved.

[thomaseizinger]

Thanks!