Fix HtmlToDjot container and list block serialization

[dereuromark]

Summary

• preserve generic HTML5 container attributes and details boundaries as tagged fenced divs instead of dropping them
• serialize list items with multiple block children using proper blank-line and continuation indentation
• add converter regressions for details, attributed HTML5 containers, multi-paragraph list items, nested blockquotes, and code blocks in list items

Testing

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

[codecov]

Codecov Report

❌ Patch coverage is 92.42424% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 93.66%. Comparing base (16db29a) to head (7ab7de6).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
src/Converter/HtmlToDjot.php	92.42%	5 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #173      +/-   ##
============================================
+ Coverage     93.62%   93.66%   +0.03%     
- Complexity     3175     3201      +26     
============================================
  Files            93       93              
  Lines          8076     8125      +49     
============================================
+ Hits           7561     7610      +49     
  Misses          515      515              

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