rework yak_result extension

[iapicca]

• [yak_utils] implemnt and test LetX and LetAsyncX
• [yak_utils] fix Cache
• [yak_utils] fix Cache (1)
• [yak_result] move thenRun extension
• [yak_runner] implement and test letRun and thenRun
• [yak_runner] update pubspec and changelog
• [yak_runner] add forEachRun
• [yak_utils] remove letAsync (it is just 'then')
• [yak_runner] bugfix for VoidResultThenRunX
• [yak_utils] bugfix for LetX
• [yak_result] rework extensions

[codecov[bot]]

Codecov Report

Merging #220 (c49cd94) into master (ba837ee) will increase coverage by 1.09%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #220      +/-   ##
==========================================
+ Coverage   92.93%   94.02%   +1.09%     
==========================================
  Files          74       70       -4     
  Lines         665      653      -12     
==========================================
- Hits          618      614       -4     
+ Misses         47       39       -8     

Impacted Files	Coverage Δ
...ackages/yak_result/lib/src/extensions/as_void.dart	100.00% <ø> (+100.00%)	:arrow_up:
packages/yak_result/lib/src/classes/success.dart	52.94% <100.00%> (ø)
...ages/yak_result/lib/src/extensions/as_success.dart	100.00% <100.00%> (ø)
packages/yak_runner/lib/src/extension/let_run.dart	100.00% <100.00%> (ø)
packages/yak_runner/lib/src/extension/run.dart	100.00% <100.00%> (ø)
...ges/yak_runner/lib/src/extension/run_delegate.dart	100.00% <100.00%> (ø)
...ackages/yak_runner/lib/src/extension/then_run.dart	100.00% <100.00%> (ø)
...s/yak_runner/lib/src/runner/value/run_nullary.dart	100.00% <100.00%> (ø)
...runner/lib/src/runner/value/run_nullary_async.dart	100.00% <100.00%> (ø)
...ges/yak_runner/lib/src/runner/value/run_unary.dart	100.00% <100.00%> (ø)
... and 7 more

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