Actually rate-limit new outbound peer connections

[teor2345]

Is your feature request related to a problem? Please describe.

Zebra has an outbound connection rate-limit in the CandidateSet. But if there haven't been many connections for a while, it can allow a very large burst of connections.

Describe the solution you'd like

• Set the current_deadline to the maximum of the current time and the next_peer_min_wait.deadline():
  

  zebra/zebra-network/src/peer_set/candidate_set.rs

  Lines 281 to 282 in 5cdcc52

  	let current_deadline = self.next_peer_min_wait.deadline();
  	let mut sleep = sleep_until(current_deadline + Self::MIN_PEER_CONNECTION_INTERVAL);

This makes sure that the next sleep is at least 100 milliseconds from the current time. (It can be be up to 200 milliseconds, if there's just been a connection, and we're about to sleep for 100 milliseconds.)

• Write proptests with random attempts and waits
  • 10 random addresses in an arbitrary AddressBook
  • 0..4 initial candidates, an async sleep from 0..400 milliseconds, and then 0..4 extra candidates
  • the first candidate should yield immediately, but we can't really test for that due to VM delays
  • each subsequent candidate should yield at least 100 milliseconds after the last candidate
  • the whole test should complete within 10 seconds (use a timeout and select)

Describe alternatives you've considered

We could change the CandidateSet.next_peer_min_wait from a Sleep to an Instant. This simplifies the code, because we're not storing a Sleep future any more. See #2160 for an example of this change.

Additional context

This change will also rate-limit the crawler task, so we should do it before #2212.