ptx accepts `--gap-size`/`--width` value exceeding `isize::MAX` while GNU `ptx` rejects

ptx accepts --gap-size/--width (-g/-w) with no upper bound and parses them into usize. A value above isize::MAX (9223372036854775807) aborts the process:

• debug / overflow-checks on: attempt to subtract with overflow (exit 101).

$ printf 'alpha beta gamma\n' > in
# debug (or release with overflow-checks on)
$ ptx --gap-size 9999999999999999999 in
thread 'main' panicked at src/uu/ptx/src/ptx.rs: attempt to subtract with overflow   # exit 101

• release (overflow-checks off): the same arithmetic wraps silently and the bad value reaches " ".repeat() / String::with_capacity(), giving capacity overflow or memory allocation … failed (reported in #12787 / #12788).

GNU ptx rejects any value exceeding isize::MAX up front with invalid gap width / invalid line width and exits 1.

$ /usr/bin/ptx --gap-size 9223372036854775807 in   # isize::MAX -> accepted
$ /usr/bin/ptx --gap-size 9223372036854775808 in   # isize::MAX + 1
ptx: invalid gap width: '9223372036854775808'      # exit 1
$ /usr/bin/ptx --width 9223372036854775808 in      # isize::MAX + 1
ptx: invalid line width: ‘9223372036854775808’     # exit 1   

Root cause

gap_size and line_width are unbounded usize fields. The chunk-sizing math then casts those usize values to isize and subtracts
them, e.g. in get_output_chunks:

// src/uu/ptx/src/ptx.rs
let half_line_size = config.line_width / 2;
let max_before_size =
    cmp::max(half_line_size as isize - config.gap_size as isize, 0) as usize;   // <- overflow
...
let max_tail_size =
    cmp::max(max_before_size as isize - before.len() as isize - config.gap_size as isize, 0) as usize;

When a value exceeds isize::MAX, the as isize cast wraps to a negative number (e.g. 9999999999999999999usize as isize == -8446744073709551617). Subtracting that negative value is effectively an addition that overflows isize.

Start in src/uu/ptx/src/ptx.rs, focusing on the option handling for --gap-size and --width and the get_output_chunks entry point. Trace how parsed usize values reach the isize arithmetic, then verify that values above isize::MAX are rejected with a nonzero exit while isize::MAX remains accepted. Add or run focused ptx coverage for both options and boundary values.