Prevent smartquotes from rewriting option dashes.

[mmulqueen]

Option names in parser-supplied text - descriptions, epilogs, and help strings - had their leading -- rewritten to an en dash in the rendered HTML, so a flag documented as --text displayed as –text. Readers copying the option out of the docs got something the command line no longer accepts.

Each --option-style token is now wrapped in an inline node that opts out via support_smartquotes, so smart quotes skips it while surrounding prose keeps normal typography.

Fixes #100

[codecov]

Codecov Report

❌ Patch coverage is 51.16279% with 21 lines in your changes missing coverage. Please review.
✅ Project coverage is 50.71%. Comparing base (f918d4e) to head (5b6de3f).

Files with missing lines	Patch %	Lines
sphinxarg/ext.py	59.45%	13 Missing and 2 partials ⚠️
test/sample-directive-smartquotes.py	0.00%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #101      +/-   ##
==========================================
+ Coverage   50.15%   50.71%   +0.56%     
==========================================
  Files          18       19       +1     
  Lines        1292     1329      +37     
  Branches      262      270       +8     
==========================================
+ Hits          648      674      +26     
- Misses        600      610      +10     
- Partials       44       45       +1     

Flag	Coverage Δ
unittests	50.48% <51.16%> (+0.56%)	⬆️

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