aead: factor apart `AeadInPlace`/`*Detached` (#1714) #2652

Job	Run time
test (1.85.0)	18s
build (1.85.0, thumbv7em-none-eabi)	17s
test (stable)	20s
build (1.85.0, wasm32-unknown-unknown)	17s
build (stable, thumbv7em-none-eabi)	10s
build (stable, wasm32-unknown-unknown)	10s
	1m 32s

Provide feedback