Fix for parallel scheduler hanging on certain types of exceptions

[alexjbush]

Description

Rework handling of exceptions to take into account fatal exceptions. This fixes the issue of some types of exceptions causing flows to hang indefinitely.

Type of change

Please delete options that are not relevant.

• [X] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] This change requires a documentation update

How Has This Been Tested?

Unit tests

[codecov-io]

Codecov Report

Merging #80 into develop will increase coverage by 0.04%. The diff coverage is 100%.

@@            Coverage Diff            @@
##           develop    #80      +/-   ##
=========================================
+ Coverage    81.95%    82%   +0.04%     
=========================================
  Files           56     56              
  Lines         1585   1589       +4     
  Branches        66     77      +11     
=========================================
+ Hits          1299   1303       +4     
  Misses         286    286

Impacted Files	Coverage Δ
...data/waimak/dataflow/ParallelActionScheduler.scala	98.27% <100%> (+0.12%)	:arrow_up:

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