tests: Add integration tests

[yohamta]

Changes

• Refactored test code and moved test DAGs into one place,internal/testdata
• Added integration tests
• Fixed pre conditions not working #810
• Fixed some data race

[codecov]

Codecov Report

Attention: Patch coverage is 47.94521% with 76 lines in your changes missing coverage. Please review.

Project coverage is 55.93%. Comparing base (39f0ce8) to head (5c80186).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/digraph/builder.go	14.28%	24 Missing ⚠️
internal/digraph/params.go	41.17%	8 Missing and 2 partials ⚠️
internal/digraph/assert.go	25.00%	6 Missing ⚠️
internal/digraph/loader.go	70.00%	6 Missing ⚠️
cmd/start_all.go	0.00%	5 Missing ⚠️
internal/client/client.go	50.00%	3 Missing and 1 partial ⚠️
cmd/scheduler.go	40.00%	3 Missing ⚠️
cmd/setup.go	57.14%	2 Missing and 1 partial ⚠️
internal/digraph/schedule.go	25.00%	3 Missing ⚠️
internal/digraph/command.go	0.00%	2 Missing ⚠️
... and 10 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #813      +/-   ##
==========================================
- Coverage   56.06%   55.93%   -0.14%     
==========================================
  Files          73       73              
  Lines        7921     7920       -1     
==========================================
- Hits         4441     4430      -11     
- Misses       3102     3110       +8     
- Partials      378      380       +2     

Files with missing lines	Coverage Δ
internal/digraph/scheduler/node.go	69.79% <100.00%> (+0.15%)	⬆️
internal/digraph/scheduler/scheduler.go	85.52% <100.00%> (+0.19%)	⬆️
internal/digraph/template.go	28.00% <100.00%> (ø)
internal/logger/context.go	65.71% <ø> (-0.96%)	⬇️
cmd/dry.go	68.00% <50.00%> (-0.84%)	⬇️
cmd/restart.go	52.89% <66.66%> (-0.68%)	⬇️
cmd/retry.go	54.05% <66.66%> (-1.21%)	⬇️
cmd/server.go	80.30% <66.66%> (-0.58%)	⬇️
cmd/start.go	63.06% <50.00%> (-0.66%)	⬇️
cmd/status.go	55.88% <66.66%> (-3.58%)	⬇️
... and 14 more

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