MAINT: drop Python 3.7 & 3.8 support due to EOL #580

Job	Run time
pytest / Determine job matrix	17s
style / Determine skipped pre-commit hooks	9s
doc / nb / Execute and build documentation	57s
doc / linkcheck / Check external links	43s
style / Run local pre-commit hooks	1m 3s
style / Run taplo through pre-commit	0s
pytest / Run unit tests (3.10, ubuntu-24.04)	1m 40s
pytest / Run unit tests (3.11, ubuntu-24.04)	1m 25s
pytest / Run unit tests (3.12, ubuntu-24.04)	1m 25s
pytest / Run unit tests (3.9, ubuntu-24.04, ampform)	4m 10s
pytest / Run unit tests (3.9, macos-14)	1m 21s
doc / Upload to GitHub Pages	0s
style / Push changes	0s
	13m 10s

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