Work around Unity's async cancellation

[sbergen]

Under certain circumstances, task cancellation in Unity will happen later in the same frame, instead of synchronously.

Due to this, state strings during errors often get updated only after the error has been propagated, causing them to be waiting ([.]) instead of canceled ([-]). This also caused the tests for Unity to have to be slightly different from .NET tests.

To work around this, we can await Task.Yield() before propagating errors.

It caused some breaking changes in RunAsLoop, which can no longer be synchronous, so I'm starting a v5 branch now, as there are other breaking changes I'd also like to make.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.90%. Comparing base (2131c5d) to head (f02afb5).
Report is 1 commits behind head on v5-base.

Additional details and impacted files

@@             Coverage Diff             @@
##           v5-base     #246      +/-   ##
===========================================
- Coverage   100.00%   99.90%   -0.10%     
===========================================
  Files          116      116              
  Lines         2177     2183       +6     
  Branches       111      113       +2     
===========================================
+ Hits          2177     2181       +4     
- Misses           0        2       +2     

Flag	Coverage Δ
Unity2021.3.27f1	99.85% <100.00%> (-0.15%)	⬇️
Unity2022.3.2f1	99.85% <100.00%> (-0.15%)	⬇️
netstandard	99.94% <100.00%> (-0.06%)	⬇️

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[sbergen]

The missing code coverage is on closing curly braces, and looks like some weirdness caused by an added await inside a catch. Couldn't figure out anything that could be done about it, so ignoring it now. 100% coverage would be nice, but this doesn't seem worth working around.