wip: add syntax highlighting with tree-sitter

[altsem]

Update: This kinda works now. Some pieces remaining:

• [x] Make it look good in any terminal (how good would a hard-coded green/red look in different kind of themes? Do we have to define entire color palettes that are not basic terminal colors?) ~- [ ] Introduce some threshold to not highlight a lot of small portions.~
• [x] Refactor the code to be more robust/performant.
• [x] Support more languages.

before: after:

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 78.39080% with 94 lines in your changes are missing coverage. Please review.

Project coverage is 86.17%. Comparing base (7a5476b) to head (0cf3c73).

Files	Patch %	Lines
src/syntax_highlight.rs	53.43%	88 Missing :warning:
src/git/diff.rs	97.30%	6 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #104 +/- ## ========================================== - Coverage 87.22% 86.17% -1.06% ========================================== Files 53 54 +1 Lines 3844 4231 +387 ========================================== + Hits 3353 3646 +293 - Misses 491 585 +94 ```

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