[#799] scheduler: fix: skipIfSuccessful skips too much

[yohamta]

The scheduler code was quite old, making it difficult to debug. So, I decided to do a major refactoring. While there are still plenty of areas for improvement, issue #799 should now be fixed.

[codecov]

Codecov Report

Attention: Patch coverage is 64.12556% with 80 lines in your changes missing coverage. Please review.

Project coverage is 56.06%. Comparing base (9344144) to head (6bb4620).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/scheduler/manager.go	68.14%	33 Missing and 3 partials ⚠️
internal/scheduler/job.go	48.00%	25 Missing and 1 partial ⚠️
internal/scheduler/scheduler.go	68.96%	15 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #811      +/-   ##
==========================================
+ Coverage   55.55%   56.06%   +0.50%     
==========================================
  Files          73       73              
  Lines        7905     7921      +16     
==========================================
+ Hits         4392     4441      +49     
+ Misses       3134     3102      -32     
+ Partials      379      378       -1     

Files with missing lines	Coverage Δ
cmd/setup.go	75.95% <100.00%> (+0.13%)	⬆️
internal/scheduler/scheduler.go	68.50% <68.96%> (+6.19%)	⬆️
internal/scheduler/job.go	44.06% <48.00%> (+44.06%)	⬆️
internal/scheduler/manager.go	68.14% <68.14%> (ø)

... and 1 file with indirect coverage changes

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