Highlight callout blocks (and theorem-like environments) the same way as fenced blocks

[maikol-solis]

Hi,

First, thanks for the extension. I'm just starting out with Neovim, and this plugin is excellent for my work.

Second, I noticed that the fenced blocks are highlighted as expected. It is a nice touch because you can see the difference between the code and regular text.

However the regular callout blocks, and the used for theorems (and other math environments), aren't highlighted properly.

Would it be possible to include them into the tree sitter grammar to differentiate them from the regular text?

Thanks for your help.

Best.

[jmbuhr]

Refs #31