fmt: `--tab-width`/`-T` has no upper bound — arithmetic overflow aborts at multiple sites (exit 134)

[leeewee]

fmt validates --width against MAX_WIDTH (2500) but applies no upper bound to --tab-width/-T. A large -T makes compute_width return a value near usize::MAX, and every arithmetic consumer of it then overflows.

Steps to reproduce

Overflow-checks build (RUSTFLAGS="-C overflow-checks=on"):

$ printf '\thello world' | fmt -T 18446744073709551615
thread 'main' panicked at src/uu/fmt/src/linebreak.rs:59:22:
attempt to add with overflow
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
Aborted (core dumped)
$ echo $?
134

site	overflow	reproducer
linebreak.rs:32:28	multiply	printf '\ta\tb\tc\n' | fmt -q -T 9223372036854775808
linebreak.rs:59:22	add	printf 'aa\n\tbb\n' | fmt -T 18446744073709551615
linebreak.rs:114:16	add	printf 'a\tbb\n' | fmt -q -T 18446744073709551615
linebreak.rs:123:8	add	printf 'a\tb\n' | fmt -q -T 18446744073709551615
linebreak.rs:126:13	add	printf 'aa\n\tbb\n' | fmt -q -c -w 1 -T 18446744073709551615
linebreak.rs:281:21	subtract	printf '\ta\tb\tc\n' | fmt -T 9223372036854775807
linebreak.rs:300:33	add	printf 'aa\n\tbb\n' | fmt -c -w 1 -T 18446744073709551615
linebreak.rs:307:24	add	printf 'a\tb\n' | fmt -T 18446744073709551615
linebreak.rs:485:23	subtract	printf 'a\tb\n' | fmt -T 9223372036854775807
parasplit.rs:234:30	multiply	printf '\t\t\tx\n' | fmt -T 9223372036854775807
parasplit.rs:459:25	add	printf '\ta\tb\tc\n' | fmt -t -T 18446744073709551615

[oech3]

By the way, GNU does not have this option. So we should simply remove this.

[oech3]

We can simplify existing upper bound by clap::value_parser!.