MNT: target py39 as new minimum, enable pyupgrade for ruff, bump min … #991

Job	Run time
Tests on 3.9 (Minimum Versions)	13m 47s
Test import order (isort)	2m 58s
Linting (Ruff)	54s
Tests on 3.9	13m 24s
Test readme renders on PyPi	14s
Tests on 3.10	15m 10s
Tests on 3.11	13m 44s
Tests on 3.12	18m 1s
Test Docs / Build Documentation	5m 13s
	1h 23m 25s

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