Refactor coroutine implementation

[dfarr]

Use channels to bind return value from yield to variables, avoids the callback style.

Closes #1

[codecov]

Codecov Report

Merging #87 (4ee4cb8) into main (dfa76d9) will decrease coverage by 2.85%.
The diff coverage is 66.25%.

@@            Coverage Diff             @@
##             main      #87      +/-   ##
==========================================
- Coverage   67.39%   64.54%   -2.85%     
==========================================
  Files          55       55              
  Lines        5824     5816       -8     
==========================================
- Hits         3925     3754     -171     
- Misses       1616     1786     +170     
+ Partials      283      276       -7     

Files	Coverage Δ
internal/app/coroutines/echo.go	100.00% <100.00%> (+18.18%)	⬆️
internal/kernel/system/system.go	73.77% <100.00%> (ø)
internal/kernel/scheduler/coroutine.go	93.10% <95.83%> (-6.90%)	⬇️
internal/kernel/scheduler/scheduler.go	95.16% <92.10%> (-4.84%)	⬇️
internal/app/coroutines/timeoutPromises.go	91.11% <80.00%> (-0.20%)	⬇️
internal/app/coroutines/deleteSubscription.go	88.09% <79.16%> (-0.28%)	⬇️
internal/app/coroutines/readSubscriptions.go	85.18% <77.14%> (-0.27%)	⬇️
internal/app/coroutines/searchPromises.go	89.74% <80.00%> (-0.13%)	⬇️
internal/app/coroutines/createSubscription.go	78.78% <83.60%> (-0.43%)	⬇️
internal/app/coroutines/timeoutPromise.go	1.92% <5.55%> (-82.99%)	⬇️
... and 6 more

... and 2 files with indirect coverage changes

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