fix: misc execution related bugs and exec updates

[jahvon]

See commit details

[codecov]

Codecov Report

Attention: Patch coverage is 38.09524% with 13 lines in your changes missing coverage. Please review.

Project coverage is 42.35%. Comparing base (441c06b) to head (43569e9).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/runner/parallel/parallel.go	33.33%	4 Missing and 2 partials ⚠️
internal/runner/serial/serial.go	33.33%	4 Missing and 2 partials ⚠️
types/executable/executable.go	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #256      +/-   ##
==========================================
- Coverage   42.37%   42.35%   -0.02%     
==========================================
  Files          91       91              
  Lines        8362     8365       +3     
==========================================
  Hits         3543     3543              
- Misses       4241     4244       +3     
  Partials      578      578              

Flag	Coverage Δ
combined	42.35% <38.09%> (-0.02%)	⬇️

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