fix: correct emoji width for table alignment

[zamderax]

Emojis were treated as width of 1 but now they should be treated as width of 2. This incorrectly would shift a row in a table off by one space.

[pepicrft]

I'd suggest to adjust the implementation to use wcwidth, which is a POSIX C function that returns the number of columns a character occupies in a terminal. Terminal, shells, and CLI tools like ls & vim use it:

#if canImport(Darwin)
import Darwin
#elseif canImport(Glibc)
import Glibc
#endif

extension Character {
    public var displayWidth: Int {
        unicodeScalars.reduce(0) { total, scalar in
            let w = wcwidth(wchar_t(scalar.value))
            // wcwidth returns -1 for non-printable, treat as 0
            return total + max(0, Int(w))
        }
    }
}

[zamderax]

Here's the problem I ran into with wcwidth

1. Emoji sequences - Characters like 👨‍👩‍👦 are actually multiple Unicode scalars joined by Zero-Width Joiners (ZWJ):
   👨 + ZWJ + 👩 + ZWJ + 👦 = 👨‍👩‍👦
2. wcwidth sees each piece separately and sums them (~8), but terminals render it as one 2-column character.
3. Variation selectors - ✓ (U+2713) vs ✓️ (U+2713 + U+FE0F). The second has a variation selector that tells the terminal "render this as emoji" (width 2), but wcwidth ignores it.
4. I put a flag emoji - 🇺🇸 is two "regional indicator" characters. wcwidth returns -1 (unknown) for each, but terminals show a single 2-column flag.

What do you think we should do?

[pepicrft]

Left a minor comment.