fuzz_seq_parse_number often hangs

e.g. in CI here: https://github.com/uutils/coreutils/actions/runs/14349472400/job/40226263754

Easy to reproduce locally with `-timeout=10`:
```
cargo +nightly fuzz run fuzz_seq_parse_number -- -max_total_time=60 -detect_leaks=0 -timeout=10
```

Looking.