chore(toolchain): pin Rust to 1.94.1 + fix CI fmt/i686 (matches sibling repos) #249

Job	Run time
nostd/thumbv6m-none-eabi/stable	36s
clippy/stable	1m 15s
Pass MSRV values to other jobs	3s
cross_test/i686-unknown-linux-gnu/stable	1m 51s
native-backend/stable	7m 47s
format/stable	33s
cross_test/s390x-unknown-linux-gnu/stable	2m 3s
docs/nightly	0s
cargo-careful	0s
miri	-1s
tests/beta	4m 59s
blas-msrv	1m 13s
tests/stable	5m 7s
tests/1.94.0	5m 2s
conclusion	-1s
	30m 27s

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