Update dev dependencies

[hmnd]

As discussed in #113. Should be merged after that.

• updated all dev dependencies, aside from eslint@9, since that may be more breaking
  • removed svelte2tsx which isn't used anywhere afaik
  • updated from svelte3 eslint tooling to svelte4
• ran prettier

[vercel]

@hmnd is attempting to deploy a commit to the Joshua Nussbaum's projects Team on Vercel.

A member of the Team first needs to authorize it.

[joshnuss]

Thanks @hmnd, looks good!

I think in the future, I should add a GitHub action to check linting of PRs.

[hmnd]

Yeah, that would be nice! eslint is currently complaining about a lot, but it's mostly just minor jsdoc formatting issues that could probably be disabled.