Fix renderer content loss in non-HTML renderers (markdown/plain/ansi)

[dereuromark]

Problem

The non-HTML renderers (markdown / plain / ansi) silently dropped content that the HTML renderer rendered correctly:

• EscapedText (e.g. an escaped literal such as a backslash-star) vanished in all three renderers. The node is not a Text subclass, so it fell through to renderChildren() and produced nothing.
• MarkdownRenderer had no Figure / Caption arms, so a captioned image glued the caption directly onto the image (e.g. i.png)Cap), and no Abbreviation arm, so the abbreviation title was lost entirely.
• A Div title attribute (set via Djot's attribute syntax, e.g. a quoted admonition title) was dropped in all three non-HTML renderers' renderDiv.

Fix

• Add an explicit EscapedText arm in each renderer. Markdown keeps the leading backslash so the literal stays literal when re-parsed as Markdown; plain/ansi emit the raw content.
• Add renderFigure (caption on its own block, with a blank line before the caption so it is not swallowed as a lazy continuation), renderCaption, and renderAbbreviation (inline abbr HTML, mirroring how subscript/superscript already fall back to inline HTML) to MarkdownRenderer.
• Preserve a Div's title attribute as a leading bold/plain line in all three renderers, guarded on a non-empty title so it is a no-op when no title is present.

Ported from carve-php commit 217b72f. The two libraries share renderer architecture; the namespaces and node APIs differ (Carve\ vs Djot\). The Div-title test uses Djot's native attribute syntax title="..." (which genuinely populates the Div title attribute) rather than carve's admonition-specific syntax.

Tests

Added tests/TestCase/Renderer/RendererContentLossTest.php covering escaped text, abbreviation title, figure/caption separation, and Div title preservation across the affected renderers. Each assertion fails on the unpatched renderers and passes with the fix.

[codecov]

Codecov Report

❌ Patch coverage is 94.44444% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.10%. Comparing base (306e362) to head (391805c).

Files with missing lines	Patch %	Lines
src/Renderer/AnsiRenderer.php	83.33%	1 Missing ⚠️
src/Renderer/MarkdownRenderer.php	95.45%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #246      +/-   ##
============================================
+ Coverage     92.06%   92.10%   +0.04%     
- Complexity     3571     3590      +19     
============================================
  Files           107      107              
  Lines         10118    10152      +34     
============================================
+ Hits           9315     9351      +36     
+ Misses          803      801       -2     

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