Use multithread executor for local imports, process imports

[bagel897]

Description

This is a rebase of changes missed in the earlier pull request

1. Adds some more documentation for how to us autoimport
2. Process the imports of init.py files only if they are in the same project or relative imports
3. Remove some non-functional code parts (IE: check_import) that no one is likely to be using yet
4. Use a multithreaded executor for local cache generation
5. Generally streamline local file management by using the module and package objects.

Checklist (delete if not relevant):

• I have made corresponding changes to library documentation for API changes