Use MaybeUninit in DecInt #4442

Job	Run time
Rustfmt	8s
Check (stable)	5m 50s
Check (nightly)	5m 54s
Check nightly-only targets (nightly)	23s
Check --no-default-features (nightly)	52s
Check (1.63)	6m 6s
Check selected Tier 3 platforms (nightly)	4m 40s
Test rustix_use_experimental_asm (powerpc64le-linux)	56s
Test (ubuntu)	42s
Test rustix_use_experimental_asm (s390x-linux)	1m 5s
Test use-libc (ubuntu)	36s
Test use-libc (i686-linux)	59s
Test (ubuntu-20.04)	42s
Test use-libc (aarch64-linux)	56s
Test use-libc (powerpc64le-linux)	54s
Test (i686-linux)	58s
Test use-libc (riscv64-linux)	56s
Test (aarch64-linux)	1m 10s
Test use-libc (s390x-linux)	1m 4s
Test (powerpc64le-linux)	1m 0s
Test use-libc (arm-linux)	53s
Test (riscv64-linux)	1m 16s
Test (s390x-linux)	1m 32s
Test (arm-linux)	1m 0s
Test (ubuntu-stable)	39s
Test (i686-linux-stable)	1m 0s
Test (aarch64-linux-stable)	52s
Test (riscv64-linux-stable)	54s
Test (s390x-linux-stable)	51s
Test (powerpc64le-linux-stable)	1m 18s
Test (arm-linux-stable)	56s
Test (ubuntu-1.63)	2m 24s
Test (i686-linux-1.63)	2m 35s
Test (aarch64-linux-1.63)	2m 38s
Test (riscv64-linux-1.63)	2m 38s
Test (s390x-linux-1.63)	2m 53s
Test (powerpc64le-linux-1.63)	2m 40s
Test (arm-linux-1.63)	2m 37s
Test (macos-latest)	29s
Test (macos-13)	50s
Test (windows)	56s
Test (windows-2019)	1m 0s
Test (musl)	38s
	1h 9m 20s

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