primefield: crate boilerplate #1990

Job	Run time
build (1.73.0, thumbv7em-none-eabi)	42s
cross (armv7-unknown-linux-gnueabihf, 1.73.0)	1m 42s
build (1.73.0, wasm32-unknown-unknown)	43s
doc	1m 5s
cross (armv7-unknown-linux-gnueabihf, stable)	1m 26s
test (i686-unknown-linux-gnu, 1.73.0, sudo apt update && sudo apt install gcc-multilib)	1m 52s
build (stable, thumbv7em-none-eabi)	32s
cross (aarch64-unknown-linux-gnu, 1.73.0)	1m 27s
test (i686-unknown-linux-gnu, stable, sudo apt update && sudo apt install gcc-multilib)	2m 48s
build (stable, wasm32-unknown-unknown)	32s
test (x86_64-unknown-linux-gnu, 1.73.0)	1m 32s
cross (aarch64-unknown-linux-gnu, stable)	1m 19s
test (x86_64-unknown-linux-gnu, stable)	1m 35s
cross (powerpc-unknown-linux-gnu, 1.73.0)	1m 30s
cross (powerpc-unknown-linux-gnu, stable)	1m 20s
	20m 5s

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