drop support for Python 3.7 #528

Job	Run time
lint	3m 16s
test (macos-latest, 3.8)	11m 46s
test (macos-latest, 3.9)	8m 21s
test (macos-latest, 3.10)	9m 2s
test (macos-latest, 3.11)	9m 4s
test (ubuntu-latest, 3.8)	5m 38s
test (ubuntu-latest, 3.9)	5m 48s
test (ubuntu-latest, 3.10)	5m 43s
test (ubuntu-latest, 3.11)	7m 5s
test (windows-latest, 3.8)	5m 53s
test (windows-latest, 3.9)	8m 42s
test (windows-latest, 3.10)	8m 25s
test (windows-latest, 3.11)	8m 25s
coverage	4m 40s
docs	3m 9s
Rust unit tests (ubuntu-latest)	6m 40s
Rust unit tests (macos-latest)	5m 16s
Rust unit tests (windows-latest)	7m 36s
Rustfmt	18s
typecheck	2m 7s
	2h 6m 54s

Provide feedback