Speedup `Uint::shr` #2020

Job	Run time
build (1.83.0, thumbv7em-none-eabi)	1m 50s
build (1.83.0, wasm32-unknown-unknown)	1m 37s
build-benchmarks	50s
careful	1m 41s
build (stable, thumbv7em-none-eabi)	1m 50s
clippy	28s
build (stable, wasm32-unknown-unknown)	1m 36s
cross (aarch64-unknown-linux-gnu, stable)	3m 50s
minimal-versions	29s
cross (powerpc-unknown-linux-gnu, stable)	5m 45s
miri (x86_64-unknown-linux-gnu)	6m 25s
rustfmt	7s
test (i686-unknown-linux-gnu, 1.83.0, sudo apt update && sudo apt install gcc-multilib)	2m 46s
miri (s390x-unknown-linux-gnu)	6m 26s
test (i686-unknown-linux-gnu, stable, sudo apt update && sudo apt install gcc-multilib)	2m 54s
test (x86_64-unknown-linux-gnu, 1.83.0)	2m 6s
doc	23s
test (x86_64-unknown-linux-gnu, stable)	2m 1s
	43m 4s

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