Use MaybeUninit in DecInt #4443

Job	Run time
Check nightly-only targets (nightly)	23s
Check (stable)	5m 36s
Check --no-default-features (nightly)	55s
Check selected Tier 3 platforms (nightly)	4m 38s
Rustfmt	4s
Check (nightly)	5m 41s
Test rustix_use_experimental_asm (powerpc64le-linux)	1m 20s
Check (1.63)	5m 50s
Test rustix_use_experimental_asm (s390x-linux)	57s
Test (ubuntu)	44s
Test use-libc (ubuntu)	37s
Test (ubuntu-20.04)	42s
Test use-libc (i686-linux)	52s
Test (i686-linux)	1m 7s
Test use-libc (aarch64-linux)	1m 3s
Test (aarch64-linux)	1m 2s
Test use-libc (powerpc64le-linux)	58s
Test (powerpc64le-linux)	1m 11s
Test use-libc (riscv64-linux)	50s
Test (riscv64-linux)	1m 3s
Test use-libc (s390x-linux)	57s
Test (s390x-linux)	1m 3s
Test (arm-linux)	54s
Test use-libc (arm-linux)	1m 3s
Test (ubuntu-stable)	37s
Test (i686-linux-stable)	1m 7s
Test (aarch64-linux-stable)	1m 0s
Test (riscv64-linux-stable)	1m 4s
Test (s390x-linux-stable)	1m 0s
Test (powerpc64le-linux-stable)	1m 8s
Test (arm-linux-stable)	58s
Test (ubuntu-1.63)	2m 23s
Test (i686-linux-1.63)	2m 39s
Test (aarch64-linux-1.63)	2m 41s
Test (riscv64-linux-1.63)	2m 37s
Test (s390x-linux-1.63)	2m 43s
Test (powerpc64le-linux-1.63)	2m 35s
Test (arm-linux-1.63)	2m 54s
Test (macos-latest)	31s
Test (macos-13)	1m 1s
Test (windows)	44s
Test (windows-2019)	1m 0s
Test (musl)	37s
	1h 8m 49s

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