Use Rust from fenix in flake #116

Job	Run time
rustfmt	19s
lint-build	2m 11s
test-flake (x86_64-unknown-linux-gnu)	7m 16s
test (stable, x86_64-unknown-linux-gnu)	4m 22s
test-flake (x86_64-unknown-linux-musl)	7m 30s
test-wasm	1m 17s
test (stable, x86_64-unknown-linux-musl)	5m 59s
test-flake (aarch64-unknown-linux-gnu)	7m 17s
test (stable, aarch64-unknown-linux-gnu)	3m 31s
test-flake (aarch64-unknown-linux-musl)	7m 3s
test (stable, aarch64-unknown-linux-musl)	4m 19s
test-flake (x86_64-apple-darwin)	11m 24s
test (stable, x86_64-apple-darwin)	11m 35s
test-flake (aarch64-apple-darwin, macos-14)	7m 29s
test (stable, x86_64-pc-windows-msvc)	9m 16s
test (stable, aarch64-apple-darwin, macos-latest, false, true, true)	5m 21s
test-projects	1m 44s
	1h 37m 53s

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