fix: add unused code allowance to multiple crates for cleaner compila… #25

Job	Run time
fmt + clippy	23s
backend features (default)	24s
parse conformance	20s
SIMD contract (Cranelift)	53s
runtime smoke	18s
type + lowering conformance	21s
backend features (llvm-backend)	1m 25s
	4m 4s

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