printf: avoid panic on i64::MIN dynamic field width

[AlejandroCoronadoN]

Summary

printf's %*d dynamic field width panics when the width argument is i64::MIN:

$ printf '%*d' -9223372036854775808 1
thread 'main' panicked at .../spec.rs: attempt to negate with overflow
$ echo $?
134

(under -C overflow-checks).

Root cause

For a negative width, resolve_asterisk_width computes the magnitude as
-(nb as isize). When nb is i64::MIN there is no positive counterpart as an
i64/isize, so the negation overflows.

Fix

Use nb.unsigned_abs() to obtain the magnitude, which is defined for i64::MIN.
The resulting width exceeds MAX_FORMAT_WIDTH, so printf now fails cleanly with
"formatting width too large" (exit 1) instead of aborting. Normal %*d widths,
including negative (left-aligned) ones, are unchanged. Adds a regression test.

Fixes #13766.

[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/misc/io-errors (fails in this run but passes in the 'main' branch)
Skipping an intermittent issue tests/tail/symlink (passes in this run but fails in the 'main' branch)
Congrats! The gnu test tests/tail/pipe-f2 is no longer failing!
Note: The gnu test tests/cut/cut-huge-range is now being skipped but was previously passing.