Make package type module

[Peeterush]

The commit Make package type module sets the package.json to type: "module", and makes the required changes throughout the codebase. This means all files now use ESM by default, and files using CJS have to be explicitly marked as such.

The commit Restore test environment reuse does just that, making npm run test run about 4 times as fast again.

The other two commits just fix some inconsistencies: a few files used double quotes and not all internal node modules imports were marked as such.

[dlemstra]

Thanks for your help. Normally I would want to have this in separate pull requests but thanks for splitting this up in separate commits. Could you amend the "Make package type module" commit and include that "Fix deno import" commit so we have a nice clean history?

[Peeterush]

Like this?

[dlemstra]

Yup, thanks!