Function shape 

pub fn shape(
    font_path: &str,
    text: &str,
    options: &str,
) -> Result<String, String>

Shapes a single input string using the same option parsing path as the CLI.

The input text is passed as Unicode codepoints so tests can include NUL bytes and other special characters without shell escaping concerns.

Errors

Returns an error string if option parsing or shaping fails.