refactor: use slice::get for clarity

[xtqqczze]

use slice::get in a few places for clarity

[sylvestre]

please update the commit message to add "why" you are doing this, thanks :)

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/pr/bounded-memory (passes in this run but fails in the 'main' branch)

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/tail/inotify-dir-recreate (fails in this run but passes in the 'main' branch)
Skipping an intermittent issue tests/date/date-locale-hour (passes in this run but fails in the 'main' branch)
Congrats! The gnu test tests/cut/bounded-memory is no longer failing!

[cakebaker]

Thanks!

[xtqqczze]

@samueltardieu perhaps there could be a clippy lint for this?

[oech3]

Mergeing this broke #11104 and author clearly knew it...