Refactor Call to include is_tail flag

The `TailCall` variant has been merged into `Call` by adding an
`is_tail` boolean field. This simplifies the AST by reducing the number
of node variants and makes it easier to handle tail call optimization.
The `tco.rs` module is responsible for setting this flag when a call
occurs in tail position.

src/ast/compiler/dumper.rs

@@ -137,23 +137,9 @@ impl Dumper {
                 self.log(&format!("Parameter (Name: '{}', Slot: {})", name.name, slot), node);
             }
 
-            BoundKind::Call { callee, args } => {
-                self.log("Call", node);
-                self.indent += 1;
-                
-                self.write_indent();
-                self.output.push_str("Callee:\n");
-                self.visit(callee);
-                
-                self.write_indent();
-                self.output.push_str("Arguments:\n");
-                self.visit(args);
-                
-                self.indent -= 1;
-            }
-            
-            BoundKind::TailCall { callee, args } => {
-                self.log("TailCall (TCO)", node);
+            BoundKind::Call { callee, args, is_tail } => {
+                let label = if *is_tail { "Call (TCO)" } else { "Call" };
+                self.log(label, node);
                 self.indent += 1;
                 
                 self.write_indent();