Refactor port scanning and improve batch size handling

[0xreacher]

Fix #1 - Wrong batch size in warning message (opts.batch_size → batch_size): The warning was showing the raw CLI value, not the actual adjusted value that ran. Users would try lowering a number that wasn't what the scanner used.

Fix #2 - or_insert_with(Vec::new) -> or_default(): Idiomatic Rust, clippy::pedantic flags the old form. Functionally identical but cleaner.

Fix #3 - scripts_to_run.clone() moved out of loop: Was cloning the entire Vec once per IP. Now iterates by reference (for script_f in &scripts_to_run) and only clones the individual ScriptFile when mutation is actually needed. Zero behavior change, much better perf at scale.

Fix #4 - Removed redundant debug!("Call format {call_f}"): The output! macro right above it already logs the full call format string. Duplicate log at a different level adds noise.

Fix #5 - usize::MAX fallback → DEFAULT_FILE_DESCRIPTORS_LIMIT: The most dangerous one. If try_into() ever failed, the returned usize::MAX would make infer_batch_size think the system has infinite file descriptors and skip all safety adjustments potentially crashing with a massive batch size. Now falls back to the same conservative 8000 limit the rest of the code uses.