[WIP] Removed code taken from core, using those features instead

[VictorKoenders]

Tracking issues:

• maybe_uninit_slice Tracking issue for #![feature(maybe_uninit_slice)] rust-lang/rust#63569
• maybe_uninit_uninit_array (no tracking issue)
• maybe_uninit_array_assume_init Tracking Issue for maybe_uninit_array_assume_init rust-lang/rust#80908

[codecov]

Codecov Report

Merging #496 (ff26bd7) into trunk (9d70b8c) will increase coverage by 0.13%.
The diff coverage is 62.50%.

@@            Coverage Diff             @@
##            trunk     #496      +/-   ##
==========================================
+ Coverage   68.35%   68.48%   +0.13%     
==========================================
  Files          43       42       -1     
  Lines        3049     3040       -9     
==========================================
- Hits         2084     2082       -2     
+ Misses        965      958       -7     

Impacted Files	Coverage Δ
src/de/mod.rs	80.00% <ø> (ø)
src/lib.rs	68.75% <ø> (ø)
src/de/impls.rs	78.31% <62.50%> (-1.48%)	⬇️

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[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[VictorKoenders]

Going to move this to #536