optimize `Array::concat` #234

Job	Run time
careful	51s
build (1.81.0, armv7a-none-eabi)	19s
build (1.81.0, thumbv7em-none-eabi)	15s
clippy	16s
doc	22s
build (1.81.0, wasm32-unknown-unknown)	16s
rustfmt	12s
build (stable, armv7a-none-eabi)	17s
test (1.81.0)	19s
build (stable, thumbv7em-none-eabi)	21s
miri (x86_64-unknown-linux-gnu)	36s
test (stable)	20s
build (stable, wasm32-unknown-unknown)	20s
miri (s390x-unknown-linux-gnu)	49s
	5m 33s

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