Moves scripts and CI/CD to nextest #501

Job	Run time
Pass MSRV values to other jobs	3s
clippy/stable	26s
nostd/thumbv6m-none-eabi/stable	18s
miri	10m 13s
cargo-careful	1m 52s
cross_test/i686-unknown-linux-gnu/stable	1m 59s
cross_test/s390x-unknown-linux-gnu/stable	8m 8s
format/nightly	18s
docs/nightly	22s
tests/nightly	2m 25s
blas-msrv	53s
tests/stable	2m 11s
tests/1.64.0	3m 7s
tests/beta	2m 14s
conclusion	3s
	34m 32s

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