Refactor backends #891

Job	Run time
Build wheels on ubuntu-latest	1m 3s
Test Docs	34s
Test Linting	12s
Build wheels on windows-latest	2m 27s
Build wheels on macos-latest	1m 40s
Build sdist	44s
Test Linux py37	50s
Test Linux py38	49s
Test Codegen	24s
Test Linux py39	51s
Test Examples	48s
Test Linux py310	55s
Test Linux py311	47s
Test Imports	16s
Test PyInstaller	1m 21s
Publish to Github and Pypi	0s
	13m 41s

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