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/main.rs

@@ -24,16 +24,16 @@ fn main() -> LoxResult<()> {
     let args: Vec<String> = env::args().collect();
     let mut lox = LoxInterpreter::new();
 
-    if args.len() > 2 {
+    let _ = if args.len() > 2 {
         eprintln!("Usage: {} [script]", args[0]);
         std::process::exit(64);
     } else if args.len() == 2 {
         // Esegui file
-        lox.run_file(&args[1])?;
+        lox.run_file(&args[1])
     } else {
         // Modalità interattiva
-        lox.run_prompt()?;
-    }
+        lox.run_prompt()
+    };
 
     Ok(())
 }
@@ -86,8 +86,9 @@ impl LoxInterpreter {
                 let mut env = Environment::new();
                 let mut interpreter = Interpreter::new(&mut env);
                 let mut result = None;
-                for stmt in stmts {
-                    result = Some(interpreter.interpret(stmt)?);
+                for (index, stmt) in stmts.iter().enumerate() {
+                    println!("executing stmt {}: {:?}", index, stmt);
+                    result = Some(interpreter.interpret(stmt.clone())?);
                 }
                 match result {
                     Some(res) => Ok(res),