numfmt: stop a clone

[oech3]

perf +2% at 9 benches

[github-actions]

GNU testsuite comparison:

Congrats! The gnu test tests/rm/many-dir-entries-vs-OOM is now passing!
Skip an intermittent issue tests/pr/bounded-memory (was skipped on 'main', now failing)

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/cut/bounded-memory (fails in this run but passes in the 'main' branch)
Note: The gnu test tests/csplit/csplit-heap is now being skipped but was previously passing.
Note: The gnu test tests/rm/many-dir-entries-vs-OOM is now being skipped but was previously passing.

[cakebaker]

Thanks!