Fix jitter calculation to match RFC3550 and convert to seconds

[yannismate]

Description

The previous jitter calculation was not following RFC3550 and reported incorrect values, as can be seen in the first modified test which reports a high jitter despite all packets arriving perfectly spaced (in both RTP timestamp and Pion receival timestamp).
Additionally, other implementations report the jitter in seconds instead of RTP timestamp units which are dependent on the streams clock rate, which should now also be the case here.

Reference issue

Fixes #234

[yannismate]

I rebased onto the current master branch which should hopefully fix the linter issue

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.60%. Comparing base (e2c357c) to head (4e37ab2).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #352      +/-   ##
==========================================
- Coverage   78.70%   78.60%   -0.10%     
==========================================
  Files          82       82              
  Lines        5165     5169       +4     
==========================================
- Hits         4065     4063       -2     
- Misses        927      931       +4     
- Partials      173      175       +2     

Flag	Coverage Δ
go	78.60% <100.00%> (-0.10%)	⬇️
wasm	76.10% <100.00%> (-0.04%)	⬇️

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

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[kevmo314]

This change seems reasonable to me, thanks!