Fix unindented paragraph absorbed into list item after nested block

[dereuromark]

Summary

Fixes #176.

When a list item contains a nested block (e.g. an indented code block) followed by a blank line and an unindented paragraph, djot-php incorrectly collected the paragraph as lazy continuation of the list item, nesting it under the last <li> instead of closing the list.

Example

1. Item 1
2. Item 2

Example

New list:

* New item 1
* New item 2

Before: New list: and the bullet list rendered inside the last <li>.
After: matches djot.js — </ol> closes, then <p>New list:</p>, then <ul>.

Fix

In BlockParser::tryParseList(), the sub-content collection loop treated any line at base indent that wasn't a block starter or matching list marker as lazy continuation. After a blank line (sawBlankLine), dropping back to base indent now breaks out with brokeForParentContent = true so the outer parser handles it as a new block.

Regression test added in NestedBlocksInListsTest::testIssue176UnindentedParagraphAfterNestedCodeBlockEndsList. Full suite (2127 tests) and PHPStan pass.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.51%. Comparing base (11f2b07) to head (c54dcc7).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #177      +/-   ##
============================================
- Coverage     93.61%   93.51%   -0.10%     
- Complexity     3241     3242       +1     
============================================
  Files            93       93              
  Lines          8203     8207       +4     
============================================
- Hits           7679     7675       -4     
- Misses          524      532       +8     

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