Plot a simulation of the congestion controller

[WesleyRosenblum]

In light of #458, which could have been easily detected with a visual representation of the congestion window, this change introduces a plot of congestion window over time for a particular simulation of the congestion controller. For now, there is just one simple simulation where in each round the full congestion window is sent and acked, but we can add more simulations in the future. In addition, I've added a snapshot test to verify nothing has changed with the output of the congestion controller.

As can be seen in the plot, the congestion window is growing linearly, when it should be growing exponentially while in slow start (see #458)

Here is another simulation, this time with Loss experienced at 3MB:

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[camshaft]

Are all of the functions available in https://crates.io/crates/libm? We might be able to include that when we're in no_std.

[camshaft]

I don't see the actual snap file anywhere. Did you forget to commit that?

[alexw91]

Codecov Report

Merging #468 (26863d8) into main (ad15171) will increase coverage by 0.03%.
The diff coverage is 55.55%.

@@            Coverage Diff             @@
##             main     #468      +/-   ##
==========================================
+ Coverage   62.98%   63.02%   +0.03%     
==========================================
  Files         205      206       +1     
  Lines        8291     8327      +36     
  Branches     2130     2134       +4     
==========================================
+ Hits         5222     5248      +26     
- Misses       1676     1683       +7     
- Partials     1393     1396       +3     

Flag	Coverage Δ
unit-tests	63.02% <55.55%> (+0.03%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...2n-quic-core/src/recovery/congestion_controller.rs	31.25% <0.00%> (-4.47%)	⬇️
quic/s2n-quic-transport/src/connection/mod.rs	0.00% <ø> (ø)
quic/s2n-quic-transport/src/recovery/mod.rs	0.00% <ø> (ø)
...uic/s2n-quic/src/provider/congestion_controller.rs	0.00% <ø> (ø)
quic/s2n-quic-core/src/recovery/cubic.rs	94.54% <100.00%> (ø)
...ic/s2n-quic-core/src/recovery/hybrid_slow_start.rs	93.10% <100.00%> (ø)
quic/s2n-quic-core/src/packet/encoding.rs	34.48% <0.00%> (-0.61%)	⬇️
quic/s2n-quic-transport/src/space/mod.rs	80.95% <0.00%> (ø)
quic/s2n-quic-core/src/crypto/key.rs	22.22% <0.00%> (+22.22%)	⬆️

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