add specialized `Buf::chunks_vectored` for `Take` #820

Job	Run time
nightly	1m 5s
rustfmt	14s
stable (ubuntu-latest)	1m 23s
minrust	1m 43s
stable (macos-latest)	1m 15s
cross (i686-unknown-linux-gnu)	31s
stable (windows-latest)	2m 25s
loom	19s
cross (armv7-unknown-linux-gnueabihf)	34s
miri	3h 33m 53s
cross (powerpc-unknown-linux-gnu)	35s
panic=abort tests	29s
cross (powerpc64-unknown-linux-gnu)	36s
tsan	1m 22s
cross (wasm32-unknown-unknown)	13s
Publish Documentation	12s
	3h 46m 49s

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