Refactor pipeline runtime code

[6543]

next step in making code more structured and maintainable

• split pipeline exec into small functions
• fix edge-cases
• have less hidden code-flows
• fix possible race condition

Test Coverage Update: pipeline/runtime

Overall: 80.5% → 98.3% (+17.8pp)

Function	main	refactor	Δ
GetShutdownCtx	0.0%	100.0%	+100.0
WithDescription	0.0%	100.0%	+100.0
makeLogger	75.0%	100.0%	+25.0
Run	74.2%	100.0%	+25.8
traceStep	84.6%	100.0%	+15.4
completeStep	—	100.0%	✱ new
executeStep	—	100.0%	✱ new
logStages	—	100.0%	✱ new
runBlockingStep	—	100.0%	✱ new
runDetachedStep	—	85.7%	✱ new
runStage	—	100.0%	✱ new
shouldSkipStep	—	100.0%	✱ new
startStep	—	100.0%	✱ new
traceWorkflowSetupError	—	100.0%	✱ new
validateConfig	—	85.7%	✱ new

[codecov]

Codecov Report

❌ Patch coverage is 96.26556% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 34.12%. Comparing base (4b4ef5e) to head (3739bcd).
⚠️ Report is 7 commits behind head on main.

Files with missing lines	Patch %	Lines
pipeline/runtime/step.go	96.12%	4 Missing and 2 partials ⚠️
pipeline/runtime/workflow.go	96.51%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6166      +/-   ##
==========================================
+ Coverage   33.84%   34.12%   +0.27%     
==========================================
  Files         422      423       +1     
  Lines       28427    28460      +33     
==========================================
+ Hits         9622     9712      +90     
+ Misses      17910    17862      -48     
+ Partials      895      886       -9     

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[qwerty287]

not sure if we wana save the flowchart somewhere? woodpecker_workflow_run_flowchart.svg

Doesn't hurt I think, maybe here? https://woodpecker-ci.org/docs/development/architecture#agent

[6543]

@qwerty287 done

[6543]

@anbraten all reviews addressed