DM-42118: Allow run-qbb to have implicit threading disabled

[timj]

Checklist

• ran Jenkins
• added a release note for user-visible changes to doc/changes

[codecov]

Codecov Report

Attention: 6 lines in your changes are missing coverage. Please review.

Comparison is base (e072a71) 87.05% compared to head (7fdcd28) 86.96%.

Files	Patch %	Lines
python/lsst/ctrl/mpexec/cli/script/run.py	33.33%	2 Missing ⚠️
python/lsst/ctrl/mpexec/cli/script/run_qbb.py	33.33%	2 Missing ⚠️
python/lsst/ctrl/mpexec/cmdLineFwk.py	50.00%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #278      +/-   ##
==========================================
- Coverage   87.05%   86.96%   -0.09%     
==========================================
  Files          49       49              
  Lines        4433     4441       +8     
  Branches      766      769       +3     
==========================================
+ Hits         3859     3862       +3     
- Misses        421      425       +4     
- Partials      153      154       +1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[erykoff]

I love this! It's belt-and-suspenders-and-braces.