Fix HtmlToDjot inline quote escaping

[dereuromark]

Summary

• escape backslashes and double quotes inside HtmlToDjot inline quote conversion so content stays valid Djot
• fix both plain quotes and cited quotes generated from ...
• add converter regressions that verify the generated Djot reparses back to HTML containing the original quoted text

Verification

• vendor/bin/phpunit tests/TestCase/Converter/HtmlToDjotTest.php
• vendor/bin/phpunit tests/TestCase/Converter/HtmlToDjotTest.php tests/TestCase/RoundTripTest.php tests/TestCase/DjotConverterTest.php
• vendor/bin/phpstan analyse src --no-progress
• vendor/bin/phpunit

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.98%. Comparing base (3a5c7f6) to head (229e718).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##             master     #169   +/-   ##
=========================================
  Coverage     93.97%   93.98%           
- Complexity     3133     3135    +2     
=========================================
  Files            93       93           
  Lines          8006     8009    +3     
=========================================
+ Hits           7524     7527    +3     
  Misses          482      482           

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

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.