feat: switch to ESM-only

[43081j]

Switches to ES modules.

Usages:

// If you're in a CJS project in Node 20 and above
const {default: picocolors} = require('picocolors');

// If you're in an ESM project in any version
import picocolors from 'picocolors';

// If you're in a CJS project before Node 20
const {default: picocolors} = await import('picocolors');

// In a browser, you can use ESM just the same
import picocolors from 'picocolors';

[43081j]

@alexeyraspopov any thoughts on this?

And rgb support

Those are the last two things people have been asking for. Happy to chat through it here, discord or email. Whatever works, but would be nice to figure it out