Add TestScheduler to support testing time-based coroutines without waiting for timeouts

[cwharris]

Description

Adds a manually driven TestScheduler that can fast-forward through delayed coroutines.

Required for nv-morpheus/Morpheus#1548

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

[mdemoret-nv]

/merge

[codecov]

Codecov Report

Merging #453 (89c299c) into branch-24.03 (2dbd985) will decrease coverage by 0.16%.
Report is 2 commits behind head on branch-24.03.
The diff coverage is 0.00%.

Additional details and impacted files

@@               Coverage Diff                @@
##           branch-24.03     #453      +/-   ##
================================================
- Coverage         73.81%   73.65%   -0.16%     
================================================
  Files               398      400       +2     
  Lines             14228    14260      +32     
  Branches           1108     1111       +3     
================================================
+ Hits              10502    10503       +1     
- Misses             3726     3757      +31     

Flag	Coverage Δ
cpp	70.16% <0.00%> (-0.18%)	⬇️
py	41.77% <0.00%> (-0.11%)	⬇️

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

Files	Coverage Δ
cpp/mrc/include/mrc/coroutines/test_scheduler.hpp	0.00% <0.00%> (ø)
cpp/mrc/src/public/coroutines/test_scheduler.cpp	0.00% <0.00%> (ø)

... and 1 file with indirect coverage changes

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