phc: migrate from `subtle` to `ctutils` #3569

Job	Run time
test (stable)	53s
test (1.85.0)	53s
minimal-versions / minimal-versions	42s
build (1.85.0, thumbv7em-none-eabi)	25s
build (stable, wasm32-unknown-unknown)	27s
build (stable, thumbv7em-none-eabi)	24s
build (1.85.0, wasm32-unknown-unknown)	29s
	4m 13s

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