GCC refactoring

[mengelbart]

Description

This PR refactors the GCC implementation using the new API introduced in #300. Currently, users are responsible for creating a SendSideController, reading CCFB reports from the attributes, and passing them to the SendSideController. This does not include pacing, which needs to be handled separately. Since the new controller does not need to read or pace outgoing packets, we no longer need the cumbersome callback API to get a pointer to the bandwidth estimator.

This refactoring also cleans up the architecture of the bandwidth estimator. It no longer uses the weird pipelining structure and no longer uses any concurrency. This should also fix/close some of the open issues and PRs like #271, #299, #260, #221, #296.

This should not be merged before #300 is merged. A follow-up PR to this one will clean up the old pkg/gcc directory to use this version.

[codecov]

Codecov Report

Attention: Patch coverage is 67.52022% with 241 lines in your changes missing coverage. Please review.

Project coverage is 70.83%. Comparing base (c06f448) to head (101c527).

Files with missing lines	Patch %	Lines
pkg/bwe/kalman.go	0.00%	66 Missing ⚠️
pkg/bwe/delay_rate_controller.go	0.00%	57 Missing ⚠️
pkg/ccfb/interceptor.go	77.44%	22 Missing and 8 partials ⚠️
pkg/bwe/send_side_bwe.go	0.00%	28 Missing ⚠️
pkg/ccfb/twcc_receiver.go	70.83%	21 Missing ⚠️
pkg/bwe/state.go	70.27%	11 Missing ⚠️
pkg/bwe/usage.go	0.00%	10 Missing ⚠️
pkg/bwe/rate_controller.go	83.33%	8 Missing ⚠️
pkg/bwe/arrival_group_accumulator.go	85.71%	3 Missing and 1 partial ⚠️
pkg/bwe/rtt.go	0.00%	3 Missing ⚠️
... and 2 more

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #306      +/-   ##
==========================================
- Coverage   71.38%   70.83%   -0.55%     
==========================================
  Files          79       97      +18     
  Lines        4526     5264     +738     
==========================================
+ Hits         3231     3729     +498     
- Misses       1158     1389     +231     
- Partials      137      146       +9     

Flag	Coverage Δ
go	70.72% <67.52%> (-0.53%)	⬇️
wasm	69.20% <67.38%> (-0.29%)	⬇️

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