Simplify code throughout + add testing notebook for codespaces #117

Job	Run time
tests (3.9, 8.0)	13s
tests (3.9, 5.7)	13s
tests (3.10, 8.0)	15s
tests (3.10, 5.7)	19s
tests (3.8, 5.7)	17s
tests (3.7, 5.7)	16s
devcontainer-build / devcontainer-build	29m 2s
	30m 35s

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