Use MaybeUninit in DecInt #4418

Job	Run time
Check --no-default-features (nightly)	55s
Check selected Tier 3 platforms (nightly)	4m 52s
Check nightly-only targets (nightly)	25s
Check (stable)	6m 18s
Rustfmt	12s
Check (nightly)	6m 6s
Check (1.63)	10m 46s
Test rustix_use_experimental_asm (powerpc64le-linux)	1m 2s
Test rustix_use_experimental_asm (s390x-linux)	1m 6s
Test use-libc (ubuntu)	44s
Test (ubuntu)	42s
Test use-libc (i686-linux)	1m 4s
Test (ubuntu-20.04)	45s
Test (i686-linux)	1m 1s
Test use-libc (aarch64-linux)	1m 6s
Test (aarch64-linux)	1m 5s
Test use-libc (powerpc64le-linux)	1m 13s
Test (powerpc64le-linux)	1m 9s
Test use-libc (riscv64-linux)	59s
Test (riscv64-linux)	1m 6s
Test use-libc (s390x-linux)	56s
Test (s390x-linux)	1m 4s
Test use-libc (arm-linux)	1m 15s
Test (arm-linux)	59s
Test (ubuntu-stable)	44s
Test (i686-linux-stable)	1m 1s
Test (aarch64-linux-stable)	1m 5s
Test (riscv64-linux-stable)	57s
Test (s390x-linux-stable)	59s
Test (powerpc64le-linux-stable)	1m 16s
Test (arm-linux-stable)	1m 6s
Test (ubuntu-1.63)	2m 17s
Test (i686-linux-1.63)	2m 28s
Test (aarch64-linux-1.63)	2m 32s
Test (riscv64-linux-1.63)	2m 37s
Test (s390x-linux-1.63)	2m 37s
Test (powerpc64le-linux-1.63)	2m 35s
Test (arm-linux-1.63)	2m 34s
Test (macos-latest)	29s
Test (macos-12)	52s
Test (windows)	48s
Test (windows-2019)	46s
Test (musl)	47s
	1h 15m 20s

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