Add cumprod #434

Job	Run time
clippy/stable	21s
format/nightly	13s
Pass MSRV values to other jobs	2s
nostd/thumbv6m-none-eabi/stable	17s
docs/nightly	24s
cross_test/s390x-unknown-linux-gnu/stable	5m 38s
cross_test/i686-unknown-linux-gnu/stable	1m 37s
miri	8m 29s
cargo-careful	2m 0s
blas-msrv	36s
tests/1.64.0	3m 37s
tests/beta	2m 41s
tests/nightly	2m 53s
tests/stable	2m 36s
conclusion	4s
	31m 28s

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