block-buffer: release v0.12.0 #381

Job	Run time
test (stable)	1m 38s
test-miri (s390x-unknown-linux-gnu)	1m 12s
test-miri (x86_64-unknown-linux-gnu)	1m 4s
test (1.85.0)	1m 31s
test-careful	1m 21s
build (stable, wasm32-unknown-unknown)	17s
minimal-versions / minimal-versions	31s
build (1.85.0, wasm32-unknown-unknown)	16s
build (1.85.0, thumbv7em-none-eabi)	20s
build (stable, thumbv7em-none-eabi)	18s
	8m 28s

Provide feedback