src: refactor builder concurrency test

[lkingland]

• 🧹 refactor build concurrency test

Expands the builder to include an optional notification channel such that temporary test tooling can be removed entirely from the builder core and logic kept in the test only.

/kind cleanup

[knative-prow]

@lkingland: The label(s) kind/cleanuo cannot be applied, because the repository doesn't have them.

In response to this:

• 🧹 refactor build concurrency test

/kind cleanuo

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[codecov]

Codecov Report

Patch coverage: 77.27% and project coverage change: +1.03 🎉

Comparison is base (8dc5a76) 62.62% compared to head (cb4a6e0) 63.66%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1821      +/-   ##
==========================================
+ Coverage   62.62%   63.66%   +1.03%     
==========================================
  Files         106      106              
  Lines       13664    13627      -37     
==========================================
+ Hits         8557     8675     +118     
+ Misses       4301     4126     -175     
- Partials      806      826      +20     

Flag	Coverage Δ
e2e-test	35.47% <0.00%> (+0.09%)	⬆️
e2e-test-oncluster	31.36% <0.00%> (+0.08%)	⬆️
e2e-test-oncluster-runtime	26.84% <0.00%> (?)
e2e-test-runtime-go	25.77% <0.00%> (?)
e2e-test-runtime-node	26.73% <0.00%> (?)
e2e-test-runtime-python	26.73% <0.00%> (?)
e2e-test-runtime-quarkus	26.85% <0.00%> (?)
e2e-test-runtime-springboot	25.91% <0.00%> (?)
e2e-test-runtime-typescript	26.85% <0.00%> (?)
integration-tests	51.70% <77.27%> (+3.45%)	⬆️
unit-tests-macos-latest	49.52% <77.27%> (-0.04%)	⬇️
unit-tests-ubuntu-latest	50.32% <77.27%> (-0.06%)	⬇️
unit-tests-windows-latest	49.53% <77.27%> (-0.07%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
pkg/oci/containerize.go	61.37% <66.66%> (+1.72%)	⬆️
pkg/oci/builder.go	78.88% <100.00%> (+1.36%)	⬆️
pkg/oci/containerize_go.go	71.81% <100.00%> (-1.34%)	⬇️

... and 5 files with indirect coverage changes

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[zroubalik]

/lgtm

[knative-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: lkingland, zroubalik

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