aead: factor apart `AeadInPlace`/`*Detached` (#1714) #3071

Job	Run time
build (1.85.0, thumbv7em-none-eabi)	1m 12s
build (1.85.0, wasm32-unknown-unknown)	1m 4s
build (stable, thumbv7em-none-eabi)	1m 18s
minimal-versions	0s
build (stable, wasm32-unknown-unknown)	1m 8s
test (1.85.0)	35s
test (stable)	26s
test (nightly)	39s
	6m 22s

Provide feedback