Fix CI: pin to Rust 1.94.0, fix clippy warnings, fix feature gates #245

Job	Run time
cross_test/i686-unknown-linux-gnu/stable	1m 52s
nostd/thumbv6m-none-eabi/stable	41s
format/stable	31s
Pass MSRV values to other jobs	3s
cross_test/s390x-unknown-linux-gnu/stable	1m 51s
clippy/stable	57s
native-backend/stable	4m 31s
miri	0s
docs/nightly	0s
cargo-careful	0s
blas-msrv	1m 13s
tests/stable	1m 10s
tests/1.64.0	59s
tests/beta	1m 6s
conclusion	-1s
	14m 53s

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