Temporary solution to handle lagged stats listeners

[josecelano]

Relates to: #1449

When I switched the channels for statistics from tokio mpsc to tokio broadcast, I introduced a bug that was only revealed after deploying the demo tracker.

The problem is that MPSC provides backpressure, so all events are processed. However, the broadcast channel has a limit, and listeners are informed with a Lagged error when the limit has been reached and events have been deleted.

We need to decide if:

1. We go back to mpsc channel
2. Or we implement another solution
3. Or we accept imprecise metrics on a high load

In the meantime, I have increased the channel capacity to be able to collect all events at the current demo peak load. That should avoid the problem of loosing events in practice.

I have also fixed the listener to handle the Lagged error. In this case, we don't have to break the loop but continue processing events to update metrics. The only difference is metrics will not be precise after this error happens because some events were lost.

[josecelano]

ACK 6fdbc47

[codecov]

Codecov Report

Attention: Patch coverage is 31.57895% with 13 lines in your changes missing coverage. Please review.

Project coverage is 84.51%. Comparing base (30684b5) to head (6fdbc47).
Report is 3 commits behind head on develop.

Files with missing lines	Patch %	Lines
...http-tracker-core/src/statistics/event/listener.rs	33.33%	3 Missing and 1 partial ⚠️
.../udp-tracker-core/src/statistics/event/listener.rs	33.33%	3 Missing and 1 partial ⚠️
...dp-tracker-server/src/statistics/event/listener.rs	33.33%	3 Missing and 1 partial ⚠️
src/bootstrap/jobs/torrent_cleanup.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1451      +/-   ##
===========================================
- Coverage    84.52%   84.51%   -0.01%     
===========================================
  Files          254      254              
  Lines        19157    19160       +3     
  Branches     19157    19160       +3     
===========================================
+ Hits         16192    16194       +2     
- Misses        2694     2695       +1     
  Partials       271      271              

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