add specialized `Buf::chunks_vectored` for `Take` #816

Job	Run time
loom	20s
miri	1h 45m 39s
minrust	1m 37s
cross (i686-unknown-linux-gnu)	31s
cross (armv7-unknown-linux-gnueabihf)	37s
nightly	17s
cross (powerpc-unknown-linux-gnu)	34s
panic=abort tests	31s
cross (powerpc64-unknown-linux-gnu)	35s
rustfmt	10s
cross (wasm32-unknown-unknown)	13s
stable (ubuntu-latest)	17s
tsan	1m 25s
stable (macos-latest)	22s
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Publish Documentation	0s
	1h 53m 33s

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