fix(numfmt): Read lines only up to null byte (as GNU does)

[FidelSch]

Fixes #11109

In cases such as "1000\x002000\n3000" numfmt outputs "1000\n3000\n", strongly suggesting it reads input until encountering a null byte, which makes sense in a C context.

Should now mimic this behavior.

Added integration tests for this as well

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/pr/bounded-memory (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/tail/follow-name (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/tail/inotify-dir-recreate (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/tty/tty-eof (passes in this run but fails in the 'main' branch)
Congrats! The gnu test tests/tail/tail-n0f is now passing!

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/pr/bounded-memory (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/tail/inotify-dir-recreate (passes in this run but fails in the 'main' branch)
Note: The gnu test tests/rm/many-dir-entries-vs-OOM is now being skipped but was previously passing.
Congrats! The gnu test tests/tail/tail-n0f is now passing!

[codspeed-hq]

Merging this PR will degrade performance by 4.27%

❌ 1 regressed benchmark
✅ 293 untouched benchmarks
⏩ 42 skipped benchmarks¹

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Simulation	shuf_input_range[1000000]	84.2 ms	88 ms	-4.27%

---

_{Comparing FidelSch:numfmt_null_byte (fb271c2) with main (ba94c69)}

Footnotes

1. 42 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/date/date-locale-hour (fails in this run but passes in the 'main' branch)
Skip an intermittent issue tests/date/resolution (fails in this run but passes in the 'main' branch)
Skipping an intermittent issue tests/tty/tty-eof (passes in this run but fails in the 'main' branch)
Congrats! The gnu test tests/rm/isatty is no longer failing!
Note: The gnu test tests/tail/pipe-f is now being skipped but was previously passing.

[cakebaker]

Thanks!