[7/n] [installinator] fix reports getting delayed

[sunshowers]

There's been a long-standing issue with the installinator where reports to wicketd get delayed quite substantially. That happens because we use one task to send reports out to every peer, blocking until all of those peers come back.

I'd assumed in the past that if installinator reached out to an unreachable peer, it would receive a TCP connection refused message, but that isn't the case -- instead, it times out. This causes reports to only be sent out roughly every 15 seconds which isn't ideal.

To fix this issue, spin up separate report tasks for each peer. Introduce separate tasks for:

• discovery (make this a persistent task that publishes updates to a watch channel)
• peer reconciliation (new peers have new report tasks spun up, while removed peers' report tasks are cancelled)
• reporting (each peer now has its own report loop)

Also simulate some kinds of network flakiness in our property-based tests.

I did a mupdate on dublin and saw that installinator reports started coming through every 2 seconds rather than every 15 or so, as expected.

Depends on:

• [1/n] [installinator] add PeerAddress wrapper #8035
• [2/n] [installinator] make some functions const #8036
• [3/n] [installinator] make DiscoverPeersError::Abort test-only #8037
• [4/n] [installinator] split fetching and progress reporting traits #8038
• [5/n] [installinator] move artifact fetch logic into its own file #8039
• [6/n] simplify FetchArtifactImpl interface #8040

[jgallagher]

Thanks for fixing this!