Use Rust from fenix in flake #115

Job	Run time
lint-build	56s
rustfmt	14s
test-flake (x86_64-unknown-linux-gnu)	1m 7s
test (1.80.1, x86_64-unknown-linux-gnu)	3m 3s
test-flake (x86_64-unknown-linux-musl)	50s
test-wasm	1m 23s
test-flake (aarch64-unknown-linux-gnu)	50s
test (1.80.1, x86_64-unknown-linux-musl)	3m 55s
test (1.80.1, aarch64-unknown-linux-gnu)	3m 42s
test-flake (aarch64-unknown-linux-musl)	50s
test (1.80.1, aarch64-unknown-linux-musl)	2m 16s
test-flake (x86_64-apple-darwin)	10m 4s
test (1.80.1, x86_64-apple-darwin)	7m 47s
test-flake (aarch64-apple-darwin, macos-14)	1m 59s
test (1.80.1, x86_64-pc-windows-msvc)	6m 57s
test (1.80.1, aarch64-apple-darwin, macos-latest, false, true, true)	4m 35s
test-projects	1m 43s
	52m 11s

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