Fix CI: pin to Rust 1.94.0, fix clippy warnings, fix feature gates #244

Job	Run time
nostd/thumbv6m-none-eabi/stable	36s
clippy/stable	52s
Pass MSRV values to other jobs	4s
native-backend/stable	7m 49s
format/stable	31s
cross_test/s390x-unknown-linux-gnu/stable	1m 42s
cross_test/i686-unknown-linux-gnu/stable	1m 45s
miri	-1s
cargo-careful	-1s
docs/nightly	-1s
blas-msrv	56s
tests/beta	1m 12s
tests/1.64.0	56s
tests/stable	1m 5s
conclusion	0s
docs/nightly	-571s
cargo-careful	-571s
format/stable	31s
native-backend/stable	7m 49s
clippy/stable	52s
miri	-571s
tests/1.64.0	1m 5s
tests/stable	1m 5s
blas-msrv	56s
tests/beta	1m 12s
nostd/thumbv6m-none-eabi/stable	36s
cross_test/s390x-unknown-linux-gnu/stable	1m 42s
cross_test/i686-unknown-linux-gnu/stable	1m 45s
Pass MSRV values to other jobs	4s
conclusion	0s
	6m 29s

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