feat(span): add to_str_range for TextSpan (#6122)

crates/cairo-lang-filesystem/src/span.rs

@@ -1,5 +1,5 @@
 use std::iter::Sum;
-use std::ops::{Add, Sub};
+use std::ops::{Add, Range, Sub};
 
 use crate::db::FilesGroup;
 use crate::ids::FileId;
@@ -94,6 +94,11 @@ impl TextSpan {
         Self { start: self.start, end: self.start }
     }
 
+    /// Returns self.start..self.end as [`Range<usize>`]
+    pub fn to_str_range(&self) -> Range<usize> {
+        self.start.0.0 as usize..self.end.0.0 as usize
+    }
+
     /// Convert this span to a [`TextPositionSpan`] in the file.
     pub fn position_in_file(self, db: &dyn FilesGroup, file: FileId) -> Option<TextPositionSpan> {
         let start = self.start.position_in_file(db, file)?;