Fix block content leaking out of marker-line nested-list items

[dereuromark]

The bug

A nested list opened on its parent item's marker line (- - A) was treated as line-scoped. The inner list was materialized from an isolated single-line slice, so its item closed immediately at the line break. As a result:

• a block placed in the inner item leaked out to the outer item, and
• a following same-indent marker fragmented the list into two separate lists.

The reference djot.js 0.3.2 keeps the inner item open: it absorbs blocks indented to its content column and continues the list across following same-indent markers. djot-php now matches that.

(carve-php inherits this parser and was affected by the same bug.)

The fix

When an item's content itself begins with a list marker (the marker-line sublist case), collect the whole nested region (lines indented past the inner marker column, plus markers sitting at it, across blank lines) into the item's lines and parse them as blocks. The existing recursive list parser then builds a persistent inner list - reusing the nested-list handling that already works for a sublist appearing on a following line, rather than adding a parallel path.

Boundary rules (verified against reference djot.js 0.3.2):

• A line indented past the inner marker column is inner-item content or a deeper sublist.
• A list marker exactly at the inner marker column continues / siblings the inner list.
• A non-marker line at the inner marker column is inner-item content only when it lazily continues an open paragraph; after a blank line (or with nothing open before it) it is outer-item content and ends the region.

Cases now matching the reference

Case 1 - input - - A\n\n block for A\n - B:

<ul>
<li>
<ul>
<li>
<p>A</p>
<p>block for A</p>
</li>
<li>
<p>B</p>
</li>
</ul>
</li>
</ul>

Case 2 - input - - A\n\n block under A (block stays inside inner item A, no leak):

<ul>
<li>
<ul>
<li>
<p>A</p>
<p>block under A</p>
</li>
</ul>
</li>
</ul>

Case 3 - input - - A\n - B\n - C (already worked, kept as a regression guard): single tight inner list [A, B, C].

Scope

• The paragraph-interrupt rule ("a list needs a blank line to follow a paragraph") is untouched.
• Bare-marker rejection is untouched.
• Single-pass parsing is preserved.
• Diff is confined to the marker-line (loose) sublist path in BlockParser::tryParseList(); a corpus diff of 33 non-marker-line list inputs shows zero output changes versus master. New tests pin Cases 1, 2, and 3 to exact HTML.

[codecov]

Codecov Report

❌ Patch coverage is 84.21053% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.34%. Comparing base (58a181a) to head (28f4ade).

Files with missing lines	Patch %	Lines
src/Parser/BlockParser.php	84.21%	6 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #251      +/-   ##
============================================
- Coverage     92.37%   92.34%   -0.04%     
- Complexity     3576     3593      +17     
============================================
  Files           107      107              
  Lines         10129    10165      +36     
============================================
+ Hits           9357     9387      +30     
- Misses          772      778       +6     

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