p224: implement `Scalar::sqrt` (#904) #45

Job	Run time
build (1.65.0, thumbv7em-none-eabi)	52s
build (1.65.0, wasm32-unknown-unknown)	49s
build (stable, thumbv7em-none-eabi)	18s
build (stable, wasm32-unknown-unknown)	16s
cross (armv7-unknown-linux-gnueabihf, 1.65.0)	2m 32s
cross (armv7-unknown-linux-gnueabihf, stable)	1m 48s
cross (aarch64-unknown-linux-gnu, 1.65.0)	2m 25s
cross (aarch64-unknown-linux-gnu, stable)	1m 55s
cross (powerpc-unknown-linux-gnu, 1.65.0)	2m 28s
cross (powerpc-unknown-linux-gnu, stable)	2m 27s
doc	25s
test (i686-unknown-linux-gnu, 1.65.0, sudo apt update && sudo apt install gcc-multilib)	2m 50s
test (i686-unknown-linux-gnu, stable, sudo apt update && sudo apt install gcc-multilib)	2m 15s
test (x86_64-unknown-linux-gnu, 1.65.0)	2m 5s
test (x86_64-unknown-linux-gnu, stable)	1m 31s
	24m 56s

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