Add cancellation capabilities to IO

[pakoito]

Make IO have a new cancellable runAsync operator that ties into the run loop for cancellation. It improves over the old way of doing it at coroutine (flatMap) boundaries because now we can cancel after every operator call instead.

I'm tempted to make the cancellable asyncRun the default, as it has the same overhead with and without it cc @raulraja for opinion.

With cancellation and parallelism we can build races, which means we can finally have a proper concurrency framework and libraries for Android!

[codecov]

Codecov Report

Merging #983 into master will increase coverage by 0.05%.
The diff coverage is 67.85%.

@@             Coverage Diff              @@
##             master     #983      +/-   ##
============================================
+ Coverage     46.99%   47.04%   +0.05%     
- Complexity      672      680       +8     
============================================
  Files           313      315       +2     
  Lines          8071     8090      +19     
  Branches        822      826       +4     
============================================
+ Hits           3793     3806      +13     
- Misses         3950     3954       +4     
- Partials        328      330       +2

Impacted Files	Coverage Δ	Complexity Δ
...ects/data/internal/BindingCancellationException.kt	100% <ø> (ø)	1 <0> (?)
...ts/src/main/kotlin/arrow/effects/internal/Utils.kt	68.96% <0%> (-11.04%)	0 <0> (ø)
...w/effects/data/internal/IOCancellationException.kt	100% <100%> (ø)	1 <1> (?)
.../arrow-effects/src/main/kotlin/arrow/effects/IO.kt	69.11% <72.72%> (+0.15%)	11 <3> (+2)	⬆️
...effects/src/main/kotlin/arrow/effects/IORunLoop.kt	74.86% <83.33%> (+1.49%)	47 <1> (+4)	⬆️
...tics/src/main/kotlin/arrow/optics/instances/map.kt	89.18% <0%> (-2.71%)	0% <0%> (ø)

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[raulraja]

Can we add this to the IO docs and a simple example of cancelation?

[pakoito]

I'll add the docs for parallelization and cancelation after the release. My plan is that because testing this is hard we'll do a beta with some maintainers and selected projects first, and promo it once it's proven to work correctly. Maybe add @experimental for now.