Add support for directory for Q-Chem

[Andrew-S-Rosen]

This PR directly follows #317 (and addresses #316) by adding a directory option for the Q-Chem custodian routines, thereby making it thread-safe and also giving the user flexibility to run beyond the current working directory.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 37.50000% with 10 lines in your changes are missing coverage. Please review.

Project coverage is 62.57%. Comparing base (9b67478) to head (d7d99af).

Files	Patch %	Lines
custodian/qchem/jobs.py	36.36%	7 Missing ⚠️
custodian/qchem/handlers.py	40.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #318      +/-   ##
==========================================
- Coverage   62.67%   62.57%   -0.10%     
==========================================
  Files          35       35              
  Lines        3003     3009       +6     
==========================================
+ Hits         1882     1883       +1     
- Misses       1121     1126       +5     

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[Andrew-S-Rosen]

@janosh --- this should be ready to go. That said, just a head's up that there seems to be a slightly flakey windows test that is seemingly unrelated to this PR.

Sometimes it fails on Windows with Python 3.10 and sometimes with Python 3.12 and then other times not at all. I have only modified Q-Chem functions, so it doesn't seem to be associated with my changes in any obvious way.