aead: factor apart `AeadInPlace`/`*Detached` (#1714) #2415

Job	Run time
minimal-versions	0s
no_std (1.85.0, thumbv7em-none-eabi)	15s
no_std (1.85.0, wasm32-unknown-unknown)	17s
test (1.85.0)	20s
test (stable)	8s
no_std (stable, thumbv7em-none-eabi)	14s
no_std (stable, wasm32-unknown-unknown)	19s
	1m 33s

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