Enforce testify/assert for tests

[RyanPotat]

Description

Use testify/assert in place of the standard testing package.

pion/.goassets#222

Reference issue

N/A

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 65.84%. Comparing base (c7c57e2) to head (b31edd8).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #200      +/-   ##
==========================================
- Coverage   65.96%   65.84%   -0.13%     
==========================================
  Files          12       12              
  Lines        1660     1660              
==========================================
- Hits         1095     1093       -2     
- Misses        464      467       +3     
+ Partials      101      100       -1     

Flag	Coverage Δ
go	65.84% <ø> (-0.13%)	⬇️
wasm	65.84% <ø> (-0.13%)	⬇️

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[JoeTurki]

This is great Ryan, thank you for doing all of this.
(Just random nitpicks but I'm going to fix them myself while updating the lint file, no worries!)