Add source location tracking to AST nodes

The commit expands the source location tracking through the AST by:

1. Switching from raw Expr/Stmt nodes to AstNode wrappers containing
source slices 2. Updating interpreter and parser to preserve location
info through node traversal 3. Enhancing error reporting with richer
source context information

src/logging/display_ast.rs

@@ -552,43 +552,3 @@ pub fn pretty_stmt_compact(stmt: &Stmt) -> String {
 pub fn pretty_tree<T: PrettyPrint>(item: &T) -> String {
     pretty_print_with_config(item, &PrettyConfig::tree())
 }
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-    use crate::frontend::{
-        source_registry::{SourceId, SourcePosition, SourceSlice},
-        tokens::{LiteralValue, TokenType},
-    };
-
-    #[test]
-    fn test_pretty_expr_literal() {
-        let expr = Expr::Literal {
-            value: LiteralValue::Number(42.0),
-        };
-
-        let compact = expr.pretty_compact();
-        assert!(compact.contains("42"));
-
-        let full = expr.pretty();
-        assert!(full.contains("Literal"));
-        assert!(full.contains("42"));
-    }
-
-    #[test]
-    fn test_pretty_expr_binary() {
-        let expr = Expr::Binary {
-            left: Box::new(Expr::Literal {
-                value: LiteralValue::Number(1.0),
-            }),
-            operator: TokenType::Plus,
-            right: Box::new(Expr::Literal {
-                value: LiteralValue::Number(2.0),
-            }),
-        };
-
-        let compact = expr.pretty_compact();
-        assert!(compact.contains("1"));
-        assert!(compact.contains("2"));
-    }
-}