use wider loads/stores in `Writer` on aarch64 #824

Job	Run time
QEMU build & test (stable, ubuntu-latest, s390x-unknown-linux-gnu, s390x-linux-gnu-gcc)	50s
Smoke-test fuzzing targets	2m 10s
QEMU build & test (stable, ubuntu-latest, i686-unknown-linux-gnu, i686-linux-gnu-gcc)	35s
Clippy	40s
Smoke-test fuzzing targets (--no-default-features --features="c-allocator")	1m 1s
Build and test (stable, ubuntu-latest, x86_64-unknown-linux-gnu)	51s
Clippy (--no-default-features --features="c-allocator")	10s
Smoke-test fuzzing targets (--no-default-features --features="rust-allocator")	50s
Build and test (msrv, ubuntu-latest, x86_64-unknown-linux-gnu)	58s
Clippy (--no-default-features --features="rust-allocator")	11s
Smoke-test fuzzing targets (stable, macos-14, aarch64-apple-darwin)	2m 6s
Build and test (beta, ubuntu-latest, x86_64-unknown-linux-gnu)	1m 3s
Build and test (stable, macos-latest, x86_64-apple-darwin)	1m 30s
dynamic library	13s
Build and test (stable, macos-14, aarch64-apple-darwin)	54s
Miri	2m 17s
wasm32	28s
Build and test (stable-x86_64-gnu, windows-2022, x86_64-pc-windows-gnu)	2m 7s
	18m 54s

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