Feature/fix esm for webpack

[rvetere]

All previous changes are upgrading the package to ESM, but it still breaks when we try to load the package as a module with the webpack loader. It is now clear that all the changes that were needed for jest are causing this. This pull request will reset the changes for jest, making it possible to load the package with webpack loader and we simply kick out jest in favor of vitest.

[jantimon]

I don’t think that a small package like css-variable should dictate the testing stack of a project

[rvetere]

i'm not talking about kicking out jest in our iso monorepo, i'm talking about switching css-variable from jest to vitest... i didn't push the changeset actually doing that yet because i still have an issue with one snapshot test after the switch