Add while loop support and token pretty printing

The commit adds while loop statements and improves token display
formatting:

- Implements while loop syntax and evaluation - Adds a new token pretty
printing module with configurable formatting - Improves token display
with colors and different output modes

src/backend/interpreter.rs

@@ -320,6 +320,17 @@ impl<'a> EvaluateInterpreter<Stmt> for Interpreter<'a> {
                     }),
                 }
             }
+            Stmt::While { condition, body } => {
+                while self.interpret(*condition.clone())?.is_truthy() {
+                    self.interpret(*body.clone())?;
+                }
+                Ok(LiteralValue::Nil)
+            }
+            Stmt::For {
+                variable,
+                iterable,
+                body,
+            } => todo!(),
         }
     }
 }