Start using extension in imports

### Description

Part of being able to build ESM variants involves being strict about the import path.
I think that you should start using the full path when importing things.

That would mean setting `import/extensions` to always error in `.js` files

### Alternatives Considered

...

### Additional Context

Part of the reason extension-less is this is working right now is b/c you are compiling from esm to commonjs

https://nodejs.org/dist/latest-v17.x/docs/api/esm.html#mandatory-file-extensions

Start by reviewing the import paths in JavaScript files and the existing `import/extensions` lint configuration. Determine the scope of enforcing full extensions for ESM-compatible imports, then verify that the lint rule passes while preserving the CommonJS compilation path.

Written by the indexing model from the issue text.