add specialized `Buf::chunks_vectored` for `Take` #809

Job	Run time
minrust	1m 37s
loom	19s
miri	2m 31s
cross (i686-unknown-linux-gnu)	36s
nightly	16s
cross (armv7-unknown-linux-gnueabihf)	33s
panic=abort tests	16s
cross (powerpc-unknown-linux-gnu)	34s
rustfmt	12s
cross (powerpc64-unknown-linux-gnu)	37s
stable (ubuntu-latest)	20s
cross (wasm32-unknown-unknown)	13s
stable (macos-latest)	22s
tsan	17s
stable (windows-latest)	29s
Publish Documentation	0s
	9m 12s

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