rejects a `-NUM` context shorthand bundled onto short options that GNU accepts

[sylvestre]

grep - rejects a -NUM context shorthand bundled onto short options that GNU accepts

Found by the differential fuzzer with args
grep ["-e", "a", "-w44ov", "-B", "1", "--null-data", "-A", "3"].

GNU grep treats a digit run inside a short-option cluster as the -NUM context shorthand:
-w2 means -w -2 (word match with two lines of context), and -w44ov means
-w -4 -4 -o -v. uu_grep only recognizes -NUM as a standalone argument, so it rejects the
bundled form with a parse error and exits 2 where GNU succeeds and exits 0.

Reproduction

Rust (incorrect)

$ printf 'x\ny\n' | ./target/release/grep -w2 x
# Output: (none)
# Stderr: error: unexpected argument '-2' found
# Exit code: 2

GNU (correct)

$ printf 'x\ny\n' | LC_ALL=C /usr/bin/grep -w2 x
# Output: (matching lines with context)
# Exit code: 0

The same happens with any short flag followed by digits, e.g. -i2:

$ printf 'x\ny\n' | ./target/release/grep -i2 x     # Rust: exit 2, "unexpected argument '-2'"
$ printf 'x\ny\n' | LC_ALL=C /usr/bin/grep -i2 x    # GNU:  exit 0

A standalone -2 already works in both (grep -2 x), so the gap is specific to the bundled
form.