Add types to tsconfig.json

[zirkelc]

Initial checklist

• I read the support docs
• I read the contributing guide
• I agree to follow the code of conduct
• I searched issues and discussions and couldn’t find anything or linked relevant results below
• I made sure the docs are up to date
• I included tests (or that’s not needed)

Description of changes

This adds "types": ["node"] to compilerOptions, so TypeScript only loads @types/node instead of every package in node_modules/@types of all parent folders.
In the micromark canary, repos are checked out inside the micromark tree, whose linter now installs @types/katex, and repos without the dom lib fail with ../../../node_modules/@types/katex/index.d.ts(142,46): error TS2304: Cannot find name 'HTMLElement'.
This repo includes the dom lib so it still passes, but in micromark/micromark#240 the maintainer asked for an explicit types field in all canary repos.
TypeScript 6 changes the default of types to [], so an explicit list is needed there anyway.
node is the only entry needed: the tests and scripts import node: modules, which without it only type check because @types/node is pulled in by references in other type packages.
I checked that npm test passes, and that the canary setup passes before and after this change.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (a758d3c) to head (0a27a8e).

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #945   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            3         3           
  Lines         1787      1787           
  Branches       123       123           
=========================================
  Hits          1787      1787           

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[remcohaszing]

Thanks!