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Add ed448 #2142

Job	Run time
build (1.81.0, thumbv7em-none-eabi)	12s
build (1.81.0, wasm32-unknown-unknown)	10s
build (stable, thumbv7em-none-eabi)	7s
build (stable, wasm32-unknown-unknown)	6s
cross (armv7-unknown-linux-gnueabihf, 1.81.0)	13s
doc	8s
cross (armv7-unknown-linux-gnueabihf, stable)	8s
cross (aarch64-unknown-linux-gnu, 1.81.0)	15s
test (i686-unknown-linux-gnu, 1.81.0, sudo apt update && sudo apt install gcc-multilib)	11s
test (i686-unknown-linux-gnu, stable, sudo apt update && sudo apt install gcc-multilib)	7s
test (x86_64-unknown-linux-gnu, 1.81.0)	9s
cross (aarch64-unknown-linux-gnu, stable)	8s
test (x86_64-unknown-linux-gnu, stable)	4s
cross (powerpc-unknown-linux-gnu, 1.81.0)	14s
cross (powerpc-unknown-linux-gnu, stable)	8s
	2m 20s

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