optimize `Array::concat` #233

Job	Run time
clippy	15s
careful	50s
build (1.81.0, armv7a-none-eabi)	18s
doc	21s
build (1.81.0, thumbv7em-none-eabi)	20s
miri (x86_64-unknown-linux-gnu)	39s
rustfmt	12s
build (1.81.0, wasm32-unknown-unknown)	16s
miri (s390x-unknown-linux-gnu)	48s
test (1.81.0)	21s
build (stable, armv7a-none-eabi)	19s
build (stable, thumbv7em-none-eabi)	18s
test (stable)	20s
build (stable, wasm32-unknown-unknown)	20s
	5m 37s

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