Implement pacing interceptor

[mengelbart]

Description

Implements a pacing interceptor separate from congestion control. The interceptor calls back to implementations of the Pacer interface whenever a packet is sent.

[codecov]

Codecov Report

❌ Patch coverage is 74.33628% with 29 lines in your changes missing coverage. Please review.
✅ Project coverage is 79.30%. Comparing base (051d2e8) to head (8a125e2).

Files with missing lines	Patch %	Lines
pkg/pacing/interceptor.go	81.55%	14 Missing and 5 partials ⚠️
pkg/pacing/rate_limit_pacer.go	0.00%	10 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #309      +/-   ##
==========================================
- Coverage   79.48%   79.30%   -0.19%     
==========================================
  Files          82       84       +2     
  Lines        4061     4174     +113     
==========================================
+ Hits         3228     3310      +82     
- Misses        662      687      +25     
- Partials      171      177       +6     

Flag	Coverage Δ
go	79.30% <74.33%> (-0.19%)	⬇️

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[JoeTurki]

We don't seem to be calling ticker.Stop()

[mengelbart]

I added a defer ticker.Stop(), although I don't think we necessarily need it since Go 1.23, because the ticker should be garbage collected when it is unreferenced, even without calling Stop. At least that's how I understand the documentation.

[JoeTurki]

I read about this, sadly. it's going to be a while before we can drop go 1.22 and 1.21 in pion, also the new behavior is eligible for collection immediately, and it doesn't say that it’s collected immediately, at least from my understanding, but i didn't test it.
Thanks.