add specialized `Buf::chunks_vectored` for `Take` #810

Job	Run time
miri	2m 27s
loom	18s
minrust	1m 35s
cross (i686-unknown-linux-gnu)	37s
cross (armv7-unknown-linux-gnueabihf)	36s
nightly	16s
panic=abort tests	16s
cross (powerpc-unknown-linux-gnu)	36s
rustfmt	10s
cross (powerpc64-unknown-linux-gnu)	36s
cross (wasm32-unknown-unknown)	12s
stable (ubuntu-latest)	20s
tsan	17s
stable (macos-latest)	28s
stable (windows-latest)	24s
Publish Documentation	0s
	9m 8s

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