High-density Unicode rendering for qrcode2.

Provides pixel types that pack 2x4 QR modules into single Unicode characters, enabling compact terminal display of QR codes.

• [BraillePixel]: Uses Braille patterns (U+2800-U+28FF), widely supported
• [OctantsPixel]: Uses Block Octant characters, requires modern fonts

Example

use qrcode2::{QrCode, EcLevel};
use qrcode_unicode_ext::BraillePixel;

let code = QrCode::new(b"Hello").unwrap();
let image = code.render::<BraillePixel>().build();
println!("{}", image);