Doctest fixes (from #139) + unblock i686 cross-tests + thumbv6m nostd build #261

Job	Run time
format/nightly	29s
nostd/thumbv6m-none-eabi/stable	33s
cross_test/i686-unknown-linux-gnu/stable	1m 50s
Pass MSRV values to other jobs	4s
native-backend/stable	8m 27s
clippy/1.94.1	42s
cross_test/s390x-unknown-linux-gnu/stable	1m 45s
docs/nightly	0s
cargo-careful	0s
miri	0s
tests/1.94.0	11m 5s
blas-msrv	1m 23s
tests/stable	11m 52s
tests/beta	12m 5s
conclusion	0s
	50m 15s

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