Render Markdig CustomContainer admonition blocks

[Copilot]

New Feature

Markdig parses fenced ::: blocks (admonitions like :::note, :::warning) into CustomContainer / CustomContainerInline AST nodes, but the renderer had no handler for them so the content was silently dropped.

What does this feature do?

Renders custom containers as a framed block with the Info label (e.g. note) on top, then the children. Inline ::tag:: spans are also rendered.

:::note
This is a *note* admonition with **bold** content.
:::

Implementation details

Followed docs/adding_a_new_renderer.md:

• Renderers (ObjectRenderers/ConsoleObjectRenderers.cs): added ConsoleCustomContainerRenderer (frame + styled Info label + children) and ConsoleCustomContainerInlineRenderer (styled inline span).
• Registration (ConsoleRenderer.cs): both registered; the inline renderer is placed before ConsoleEmphasisInlineRenderer since CustomContainerInline : EmphasisInline and Markdig picks the first assignable renderer.
• DisplayOptions: three new TextStyle properties — CustomContainer (body), CustomContainerInfo (label), CustomContainerInline — defaulting to bold for the labels and unstyled for the body. Clone() updated accordingly.
• Tests: new customContainer.md / .txt fixture, two RendererTests_CustomContainer* style assertions, and the three styles added to m_crazyOptions.
• Bracket escaping: extended bracketEscaping.md with [test27]–[test29] exercising both block and inline containers; .txt regenerated.
• Example doc: new "Custom Containers (Admonitions)" section in example.md.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.71%. Comparing base (55c3cc5) to head (1f167df).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #132      +/-   ##
==========================================
+ Coverage   95.64%   95.71%   +0.07%     
==========================================
  Files          28       29       +1     
  Lines        1606     1635      +29     
  Branches      171      172       +1     
==========================================
+ Hits         1536     1565      +29     
  Misses         46       46              
  Partials       24       24              

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[boxofyellow]

@copilot Please address this comment.

Additionally, I have added a new step to guide doc https://github.com/boxofyellow/ConsoleMarkdownRenderer/blob/main/docs/adding_a_new_renderer.md for updating the changelog. Please apply those changes within this PR as well.

[Copilot]

@copilot Please address this comment.

Additionally, I have added a new step to guide doc https://github.com/boxofyellow/ConsoleMarkdownRenderer/blob/main/docs/adding_a_new_renderer.md for updating th...

Added a changelog entry for this PR under ## Upcoming Changes → ### :art: Renderers :art: in docs/CHANGELOG.md (with the before/after image placeholders) in 05481b4.