add spec for sweepable pipeline

[LittleLittleCloud]

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• There's a descriptive title that will make sense to other developers some time from now.
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• Your change description explains what the change does, why you chose your approach, and anything else that reviewers should know.
• You have included any necessary tests in the same PR.

[codecov]

Codecov Report

Merging #6218 (805ebb3) into main (85a9d9e) will decrease coverage by 0.00%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #6218      +/-   ##
==========================================
- Coverage   68.33%   68.33%   -0.01%     
==========================================
  Files        1102     1102              
  Lines      242323   242323              
  Branches    25174    25174              
==========================================
- Hits       165601   165593       -8     
- Misses      70156    70163       +7     
- Partials     6566     6567       +1     

Flag	Coverage Δ
Debug	68.33% <ø> (-0.01%)	⬇️
production	62.77% <ø> (-0.01%)	⬇️
test	88.85% <ø> (ø)

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

Impacted Files	Coverage Δ
...c/Microsoft.ML.FastTree/Utils/ThreadTaskManager.cs	79.48% <0.00%> (-20.52%)	⬇️