chore: Remove usage of `six` package #370

Job	Run time
Lint (Python 3.10 on ubuntu-latest)	1m 3s
Test (Python 3.8 on macos-latest)	7s
Test (Python 3.9 on macos-latest)	6s
Test (Python 3.10 on macos-latest)	7s
Test (Python 3.11 on macos-latest)	7s
Test (Python 3.12 on macos-latest)	7s
Test (Python 3.8 on ubuntu-latest)	36s
Test (Python 3.9 on ubuntu-latest)	38s
Test (Python 3.10 on ubuntu-latest)	38s
Test (Python 3.11 on ubuntu-latest)	43s
Test (Python 3.12 on ubuntu-latest)	40s
Test (Python 3.8 on windows-latest)	2m 37s
Test (Python 3.9 on windows-latest)	2m 11s
Test (Python 3.10 on windows-latest)	3m 26s
Test (Python 3.11 on windows-latest)	2m 53s
Test (Python 3.12 on windows-latest)	2m 56s
	18m 55s

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