feat(parser): Enable Markdig Mathematics extension

[abap34]

Thank you for your continued maintenance work! I use marksman heavily for note-taking, and it has been extremely helpful.

Summary

As reported in #326, marksman currently produces incorrect diagnostics inside math blocks.
For example, bracket pairs can be interpreted as links (including wiki-links), which results in false, non-existent errors.

Another example (wiki-link):

To address this, this PR enables Markdig’s Mathematics extension via .UseMathematics().
This should make marksman treat $...$ / $$...$$ regions as math and avoid applying link parsing and link-related diagnostics inside them, reducing false reports.

Notes

This is a breaking change. However, I personally could not think of any content inside math blocks that should be treated or checked as links or something. I also suspect there are other link-like patterns in math blocks that currently trigger unnecessary checks, and enabling the math extension should help avoid those as well.

If there is a reason why marksman has intentionally not enabled this extension so far, please feel free to close this PR.

Closes #326