Partial migration to `rand_core` v0.9 #2697

Job	Run time
build (1.81.0, thumbv7em-none-eabi)	16s
test (1.81.0)	19s
build (1.81.0, wasm32-unknown-unknown)	15s
test (stable)	30s
build (stable, thumbv7em-none-eabi)	9s
build (stable, wasm32-unknown-unknown)	34s
	2m 3s

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