Test several backends (tensorflow + pytorch) #390

Job	Run time
linters	18s
type-checking	26s
tests (3.9, ubuntu-latest, true, tf)	17m 5s
tests (3.9, ubuntu-latest, true, torch)	8m 34s
tests (3.9, macos-latest, true, tf)	17m 54s
tests (3.9, macos-latest, true, torch)	12m 18s
tests (3.9, windows-latest, true, tf)	15m 25s
tests (3.9, windows-latest, true, torch)	8m 18s
tests (3.11, ubuntu-latest, true, tf)	13m 22s
tests (3.11, ubuntu-latest, true, torch)	7m 33s
tests (3.11, macos-latest, true, tf)	20m 13s
tests (3.11, macos-latest, true, torch)	8m 21s
tests (3.11, windows-latest, true, tf)	16m 39s
tests (3.11, windows-latest, true, torch)	8m 21s
build-doc / build-doc	1m 8s
deploy-doc	0s
	2h 35m 55s

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