inout: add `From` impl for splitting `[T; N * M]` into `[[T; N]; M]` … #1303

Job	Run time
windows (x86_64-pc-windows-gnu, 1.85.0)	42s
macos (stable)	15s
windows (x86_64-pc-windows-gnu, stable)	1m 23s
linux (i686-unknown-linux-gnu, 1.85.0, sudo apt update && sudo apt install gcc-multilib)	27s
linux (x86_64-unknown-linux-gnu, stable)	17s
cross (aarch64-unknown-linux-gnu, 1.85.0)	39s
linux (x86_64-unknown-linux-gnu, 1.85.0)	17s
linux (i686-unknown-linux-gnu, stable, sudo apt update && sudo apt install gcc-multilib)	39s
minimal-versions / minimal-versions	24s
cross (aarch64-unknown-linux-gnu, stable)	49s
macos (1.85.0)	22s
build-only	17s
	6m 31s

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