Fix Unfalsifiable Signal Test

[MattToast]

Fixes unfalsifiable test that tests SmartSim's custom SIGINT signal handler. Adds infrastructure to make the test pass again.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 90.76%. Comparing base (d462fd2) to head (bbd3f5c).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #535      +/-   ##
===========================================
+ Coverage    90.70%   90.76%   +0.06%     
===========================================
  Files           65       65              
  Lines         4498     4528      +30     
===========================================
+ Hits          4080     4110      +30     
  Misses         418      418              

Files	Coverage Δ
smartsim/_core/control/controller.py	85.91% <100.00%> (ø)
smartsim/_core/control/jobmanager.py	94.15% <ø> (-0.04%)	:arrow_down:
smartsim/_core/utils/helpers.py	93.70% <100.00%> (+1.74%)	:arrow_up: