added astype for sparse spin matrices #1500

Job	Run time
runnable	0s
lint / lint	23s
test (3.9, true, true, ubuntu-latest)	8m 57s
test (3.9, true, true, macos-13)	13m 59s
test (3.9, true, false, ubuntu-latest)	8m 19s
test (3.9, true, false, macos-13)	19m 18s
test (3.9, true, false, macos-latest)	8m 26s
test (3.9, false, false, ubuntu-latest)	7m 28s
test (3.9, false, false, macos-13)	10m 2s
test (3.9, false, false, macos-latest)	5m 35s
test (3.13, true, false, ubuntu-latest)	11m 44s
test (3.13, true, false, macos-13)	20m 52s
test (3.13, true, false, macos-latest)	8m 51s
	2h 3m 54s

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