Keep inline code pipes inside markdown table cells

[AnkanMisra]

Summary

Fixes markdown table rendering when inline code spans contain pipe characters. Code such as `a|b` and `a||b` now stays in one table cell instead of being split into extra columns.

Why

Agent output and markdown previews can include regexes, shell snippets, and other code spans with | characters inside tables. Before this change, those pipes could be parsed as table delimiters even though they were part of inline code.

Changes

• Masks raw pipes only inside matched inline code spans before pulldown-cmark parses tables.
• Restores rendered code-span text from the original source range, including escaped table pipes.
• Avoids masking unmatched backticks, fenced code blocks, indented code blocks, and invalid fence closers.
• Adds parser and renderer coverage for raw pipes, escaped pipes, unmatched inline code, invalid fences, and code-span link callbacks.

Manual check: generated agent responses across multiple models render tables containing `a|b`, `(a|b)`, and `a||b` as single code-span cells rather than split columns.

Screenshots / Recordings

Before	After

Self-Review Checklist

• I've reviewed my own diff for quality, security, and reliability
• Unsafe blocks (if any) have justifying comments
• The content is consistent with the UI/UX checklist
• Tests cover the new/changed behavior
• Performance impact has been considered and is acceptable

Closes #57683

Release Notes:

• Fixed markdown table rendering for inline code spans that contain pipe characters.

[smitbarmase]

Thanks,@tomhoule and I decided to go forward with only the GFM approach, i.e., rendering \| as | in tables, but we don't think we need a more generic case for now, since it introduces a lot of complexity and maintainability burden. I think this should be enough for most cases. Thanks again.