refactor: remove unnecessary python 2 deps/syntax

[andrewleap-optimizely]

Summary

• Updated format functions to f-strings
• Removed unnecessary dependencies
• Removed redundant super parameters and object baseclass
• Removed deprecated threading method
• Removed unnecessary py2 patches
• Updated setup.py versions

Modernize syntax, increase readability, decrease non standard library dependencies

[Mat001]

1. Have you ran the linter?
2. pypy tests on CI are failing, I guess that's because this branch doesn't have the fix for pypy yet?

Approved, but pls check out the comments.