Doctest fixes (from #139) + unblock i686 cross-tests + thumbv6m nostd build #263

Job	Run time
nostd/thumbv6m-none-eabi/stable	33s
clippy/1.94.1	42s
Pass MSRV values to other jobs	3s
cross_test/i686-unknown-linux-gnu/stable	11m 36s
format/nightly	30s
cross_test/s390x-unknown-linux-gnu/stable	17m 0s
native-backend/stable	7m 56s
docs/nightly	0s
cargo-careful	0s
miri	0s
tests/beta	11m 25s
blas-msrv	1m 0s
tests/stable	10m 51s
tests/1.94.0	9m 13s
conclusion	0s
	1h 10m 49s

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