Fix quadratic rendering time for many inline links

[aryansk]

Description

Rendering a paragraph containing many inline links took quadratic time:
each match replaced the link with a placeholder and then rescanned the
whole remaining text from index 0, so N links cost O(N²) pattern work.
'[link](x)' * 8192 took ~7s before this change and ~0.3s after.

__applyPattern now returns the index just past the inserted placeholder
so the next scan starts at the unprocessed tail.

Fixes #1619.

AI Assistance Disclosure

• If AI tools were used, I have disclosed which ones, and fully reviewed and verified their output.

Claude (via Command Code) assisted with implementation and testing; the change was fully reviewed and verified by a human.

Checklist

• This PR follows the contribution guidelines.
• The code follows the Code Style Guide.
• The commit message follows the Commit Message Style Guide.
• I have added or updated relevant docs, including release notes if applicable.
• I have added or updated relevant tests.
• I have not requested, and will not request, an automated AI review for this PR.

[waylan]

Thanks for working on this. I have a few concerns as outlined below.

[aryansk]

Thanks for the detailed review. Commit b745bba addresses the points raised: it removes the wall-clock regression test, replaces it with a deterministic search-offset assertion, and moves #1619 under Unreleased > Changed to document the inline-processor behavior/API impact. The full unittest suite passes with 1,089 tests and 13 skipped; changed-file flake8 and git diff --check pass.

[waylan]

Thank you for addressing my concerns. I am going to let @facelssuser review this as he has a better grasp of the affected code.

[aryansk]

Thanks, @waylan. I appreciate the follow-up; I’ll wait for @facelssuser’s review of the affected code.

[facelessuser]

I will hopefully get to this sometime this week. I've become somewhat exhausted with the onslaught of everyone pointing AI at every project on the internet. I'm already dealing with similar issues on numerous projects I support.

[aryansk]

Understood. I will leave the draft unchanged while you assess it; no further follow-up is needed from me right now.

[NOVATechnocrat]

Thanks for all of your your hard work, I know you all are busy. Let me know if I can assist.