Modernize the package

[mourner]

@Komzpa If we're reviving the project bit by bit, I'd love to do a modernization pass on this — the current setup is super ancient. At the minimum:

• Get rid of all the legacy cruft like Grunt, JSHint, Uglify etc
• Use ES classes and ES modules with named exports instead of global object namespacing
• Use native Node test runner
• Use modern ESLint
• Use TypeScript types, either natively or via JSDoc comment types
• Use Rolldown for efficient bundling

Let me make a pass, should be quick.

[Komzpa]

@mourner I'm now low on tokens till Wednesday, you can make a pass and I'll continue later next week on whatever's left in org's tickets/pr's afterwards.