REF: Remove side effects from importing Styler 2
draft

Alongside this PR I would also recommend:

 - [ ] deprecating `Styler.from_custom_template` since it will be more featureful to create a class directly with specified new templates, and basically just as easy. Docs could be updated.
@rhshadrach I created this versus your original PR, to remove some of the floating class attribute caches.

One or two things to clean up test wise but I think it preserves almost all functionality whilst achieving the import side effects changes. Sounds good! This pull request is stale because it has been open for thirty days with no activity. Please [update](https://pandas.pydata.org/pandas-docs/stable/development/contributing.html#updating-your-pull-request) and respond to this comment if you're still interested in working on this. Are you still working on this @attack68? I looked at this yesterday coincidentally actually. Last I checked this works locally but I couldnt get the tests to pass online because they read a file and I guess there is something wrong with the paths. This was quite a good PR though just havent had time to push it over the edge. Closing to clear the queue, but when you have time to come back to this feel free to reopen the PR