conditional import `scipy_fft` #522

Job	Run time
build_windows (3.9)	5m 6s
build_linux (3.9)	2m 42s
build_windows (3.10)	5m 5s
build_windows (3.11)	4m 54s
build_windows (3.12)	5m 5s
build_linux (3.10)	2m 55s
build_linux (3.11)	2m 13s
build_linux (3.12)	2m 10s
test_linux (3.9, false, ubuntu-latest)	1m 27s
test_linux (3.10, false, ubuntu-latest)	1m 34s
test_linux (3.11, false, ubuntu-latest)	2m 26s
test_linux (3.12, false, ubuntu-latest)	1m 12s
test_windows	0s
	36m 49s

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