🔧 More improvements for directive option parsing

[chrisjsewell]

No description provided.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 94.28571% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 90.13%. Comparing base (8614eca) to head (8cd5441).

Files	Patch %	Lines
myst_parser/parsers/options.py	92.30%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #919      +/-   ##
==========================================
- Coverage   90.14%   90.13%   -0.02%     
==========================================
  Files          24       24              
  Lines        3400     3415      +15     
==========================================
+ Hits         3065     3078      +13     
- Misses        335      337       +2     

Flag	Coverage Δ
pytests	90.13% <94.28%> (-0.02%)	⬇️

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