`aarch64` backend implementation #200

Job	Run time
Fuzz	33s
Clippy	27s
docs	18s
feature checks	27s
fmt	17s
Miri (x86_64-unknown-linux-gnu, --no-default-features)	54s
Miri (x86_64-unknown-linux-gnu)	1m 20s
Miri (x86_64-unknown-linux-gnu, --all-features)	1m 5s
Miri (aarch64-unknown-linux-gnu, --no-default-features)	48s
Miri (aarch64-unknown-linux-gnu)	52s
Test (x86_64-unknown-linux-gnu, nightly)	26s
Test (x86_64-unknown-linux-gnu, beta)	29s
Test (x86_64-unknown-linux-gnu, stable)	29s
Test (x86_64-unknown-linux-gnu, 1.64)	27s
Test (aarch64-unknown-linux-gnu, nightly)	1m 6s
Test (aarch64-unknown-linux-gnu, beta)	41s
Test (aarch64-unknown-linux-gnu, stable)	55s
Test (aarch64-unknown-linux-gnu, 1.64)	52s
Outdated	0s
	12m 26s

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