Fix: Parse boolean literals as identifiers

Boolean literals `true` and `false` are now parsed as identifiers,
matching the behavior of other constants like `NaN`. This change aligns
the AST representation of boolean literals with their runtime constants.

src/ast/rtl/core.rs

@@ -16,6 +16,8 @@ fn register_constants(env: &Environment) {
     
     // We register NaN as a value, not a function.
     env.register_constant("NaN", StaticType::Float, Value::Float(f64::NAN));
+    env.register_constant("true", StaticType::Bool, Value::Bool(true));
+    env.register_constant("false", StaticType::Bool, Value::Bool(false));
 }
 
 fn register_arithmetic(env: &Environment) {