Function assign_values 

pub fn assign_values(
    file: &mut PolydatFile,
    assignments: &[(String, String)],
) -> Result<(), String>

Assign name=value text to externs and inputs by rewriting their declarations.

• An extern name: T gets "value" as its default. The compiler fuses the string literal to T through the same coercions that apply when a str wire feeds a typed port, so a bad value is a compile error carrying the program’s own diagnostic.
• An input name: T becomes extern name: T = "value": for this run the coordinate is fixed, so it is no longer a coordinate.
• A name that is neither is an error listing what the program declares.

The transform is order preserving and leaves every other statement untouched.