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Moves scripts and CI/CD to nextest #493

Job	Run time
Pass MSRV values to other jobs	3s
nostd/thumbv6m-none-eabi/stable	19s
clippy/stable	32s
format/nightly	15s
miri	3m 1s
cargo-careful	2m 28s
cross_test/s390x-unknown-linux-gnu/stable	8m 2s
cross_test/i686-unknown-linux-gnu/stable	2m 53s
docs/nightly	23s
blas-msrv	1m 13s
tests/beta	2m 38s
tests/nightly	3m 4s
tests/stable	2m 34s
tests/1.64.0	5m 20s
conclusion	4s
	32m 49s