JitterBuffer: Improve performance for SampleBuilder use

[thatsnotright]

Description

This PR Should hopefully improve the performance for use by SampleBuilder and in the general case.

@at-wat If you have time would you be able to test this PR and the corresponding branch I created in the webrtc repository? pion/webrtc#2959

Thank you!

[codecov]

Codecov Report

Attention: Patch coverage is 83.50000% with 66 lines in your changes missing coverage. Please review.

Project coverage is 78.55%. Comparing base (149728f) to head (2de1b4e).

Files with missing lines	Patch %	Lines
pkg/jitterbuffer/rbtree.go	84.26%	45 Missing and 11 partials ⚠️
pkg/jitterbuffer/jitter_buffer.go	61.53%	5 Missing ⚠️
pkg/jitterbuffer/receiver_interceptor.go	80.00%	4 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #292      +/-   ##
==========================================
+ Coverage   78.52%   78.55%   +0.02%     
==========================================
  Files          81       82       +1     
  Lines        5136     5520     +384     
==========================================
+ Hits         4033     4336     +303     
- Misses        928     1000      +72     
- Partials      175      184       +9     

Flag	Coverage Δ
go	78.44% <83.50%> (-0.09%)	⬇️
wasm	76.35% <83.50%> (+0.19%)	⬆️

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[at-wat]

I'll try it later!

[at-wat]

@thatsnotright I tested this branch locally in my usecase and confirmed that SampleBuilder's performance is good! (mostly same CPU/memory usage as the latest release)

[thatsnotright]

@thatsnotright I tested this branch locally in my usecase and confirmed that SampleBuilder's performance is good! (mostly same CPU/memory usage as the latest release)

@at-wat Thank you for taking the time to test, I appreciate your time! I'll clean up the code a little and make some test coverage improvements and then work with @Sean-Der on next steps!