changed: sparse backends default to post-processing #1742

Job	Run time
Julia 1 - ubuntu-latest - x64 - pull_request	1h 25m 27s
Julia pre - ubuntu-latest - x64 - pull_request	1h 16m 15s
Julia lts - ubuntu-latest - x64 - pull_request	43m 7s
	3h 24m 49s

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