Add syntax highlight via tree-sitter-highlight

[LucasPickering]

Description

Describe the change. If there is an associated issue, please include the issue link (e.g. "Closes #xxx"). For UI changes, please also include screenshots.

Add syntax highlighting to the three places where we show bodies: Recipe pane, Request tab, Response Body tab.

This took a lot of fucking around to maintain template preview styles on top of syntax highlighting.

Closes #264

Known Risks

What issues could potentially go wrong with this change? Is it a breaking change? What have you done to mitigate any potential risks?

There's almost definitely bugs in here. There's even some weird stuff that may be bugs but I'm choosing to ignore. I did my best to make sure there's no dramatic perf impact or crashes, so anything else negative is not going to be an obstruction, and is most likely fixable later.

QA

How did you test this?

Added a couple unit tests, tested various scenarios in the TUI. Definitely under tested, but like I said above, I'm fairly confident it doesn't break anything and the rest is just bonus.

Checklist

• Have you read CONTRIBUTING.md already?
• Did you update CHANGELOG.md?
  • Only user-facing changes belong in the changelog. Internal changes such as refactors should only be included if they'll impact users, e.g. via performance improvement.
• Did you remove all TODOs?
  • If there are unresolved issues, please open a follow-on issue and link to it in a comment so future work can be tracked