cpubits: add expression example (#1422) #69

Job	Run time
test-cross (armv7-unknown-linux-gnueabi)	1m 0s
test-cross (powerpc-unknown-linux-gnu)	1m 15s
test (i686-unknown-linux-gnu, ubuntu-latest, 1.85.0, sudo apt update && sudo apt install gcc-mult...	33s
test (x86_64-apple-darwin, macos-latest, 1.85.0)	24s
test (x86_64-pc-windows-msvc, windows-latest, 1.85.0)	37s
test-wasm (1.85)	17s
test (x86_64-unknown-linux-gnu, ubuntu-latest, 1.85.0)	14s
test-wasm (stable)	15s
	4m 35s

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