Fix nested blockquotes and code blocks in list items

[dereuromark]

Summary

Fixes #83 - Blockquotes and code blocks in lists don't get rendered properly.

• Detects when list item content starts with a block element marker and parses it as blocks instead of inline text
• Calculates proper content indent based on list type (ordered lists use actual marker width, bullet/task lists use base marker width)
• Adds comprehensive test coverage for nested blocks in lists

Changes

The parser was treating all multi-line list item content as paragraph text, which caused blockquotes (>) and code fences (```) to be escaped/misrendered instead of being parsed as proper block elements.

The fix modifies BlockParser::tryParseList() to:

1. Check if the first line of list item content starts with a block element using isBlockElementStart()
2. If so, pass content to parseBlocks() instead of treating it as inline paragraph text
3. Calculate proper content indent based on marker width (fixes ordered list continuation lines)

Examples

Before:

<ul><li><p>&gt; This is a quote</p></li></ul>

After:

<ul><li><blockquote><p>This is a quote</p></blockquote></li></ul>

[dereuromark]

Note: The Coding Standards CI failure is due to pre-existing PHPStan errors in InlineParser.php (not modified by this PR). The master branch also fails CI with the same errors. All test jobs pass successfully.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.86%. Comparing base (1a6eafc) to head (2269205).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##             master      #84   +/-   ##
=========================================
  Coverage     93.85%   93.86%           
- Complexity     2130     2132    +2     
=========================================
  Files            77       77           
  Lines          5699     5705    +6     
=========================================
+ Hits           5349     5355    +6     
  Misses          350      350           

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