Doctest fixes (from #139) + unblock i686 cross-tests + thumbv6m nostd build #262

Job	Run time
format/nightly	30s
cross_test/i686-unknown-linux-gnu/stable	2m 9s
cross_test/s390x-unknown-linux-gnu/stable	2m 23s
nostd/thumbv6m-none-eabi/stable	34s
clippy/1.94.1	43s
native-backend/stable	7m 43s
Pass MSRV values to other jobs	3s
miri	0s
cargo-careful	0s
docs/nightly	0s
tests/beta	10m 56s
blas-msrv	1m 4s
tests/stable	10m 30s
tests/1.94.0	10m 46s
conclusion	0s
	47m 21s

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