Partial migration to `rand_core` v0.9 #2695

Job	Run time
test (1.81.0)	19s
test (stable)	13s
build (1.81.0, thumbv7em-none-eabi)	17s
build (1.81.0, wasm32-unknown-unknown)	16s
build (stable, thumbv7em-none-eabi)	8s
build (stable, wasm32-unknown-unknown)	9s
	1m 22s

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