Refactor random number generation to factory

- Use a `make-random` factory to create isolated random number
  generators.
- Remove the global `prng` from the `Environment`.
- Ensure `make-random` can be called with or without a seed.

src/ast/rtl/math.rs

@@ -135,27 +135,39 @@ pub fn register(env: &Environment) {
         best
     });
 
-    // Random
-    let random_ty = StaticType::Function(Box::new(Signature {
+    // Random generator factory (Closure-based)
+    let generator_sig = Signature {
         params: StaticType::Tuple(vec![]),
         ret: StaticType::Float,
-    }));
+    };
+    
+    let make_random_ty = StaticType::FunctionOverloads(vec![
+        Signature {
+            params: StaticType::Tuple(vec![]),
+            ret: StaticType::Function(Box::new(generator_sig.clone())),
+        },
+        Signature {
+            params: StaticType::Tuple(vec![StaticType::Int]),
+            ret: StaticType::Function(Box::new(generator_sig)),
+        },
+    ]);
 
-    let prng = env.prng.clone();
-    env.register_native_fn("random", random_ty, Purity::SideEffectFree, move |_| {
-        Value::Float(prng.borrow_mut().f64())
-    });
-
-    let seed_ty = StaticType::Function(Box::new(Signature {
-        params: StaticType::Tuple(vec![StaticType::Int]),
-        ret: StaticType::Void,
-    }));
-
-    let prng_seed = env.prng.clone();
-    env.register_native_fn("seed!", seed_ty, Purity::Impure, move |args| {
-        if let Value::Int(s) = args[0] {
-            prng_seed.borrow_mut().seed(s as u64);
-        }
-        Value::Void
+    env.register_native_fn("make-random", make_random_ty, Purity::SideEffectFree, |args| {
+        let rng = if args.is_empty() {
+            fastrand::Rng::new()
+        } else if let Value::Int(s) = args[0] {
+            fastrand::Rng::with_seed(s as u64)
+        } else {
+            fastrand::Rng::new()
+        };
+        
+        let prng = std::rc::Rc::new(std::cell::RefCell::new(rng));
+        
+        Value::Function(std::rc::Rc::new(crate::ast::types::NativeFunction {
+            func: std::rc::Rc::new(move |_| {
+                Value::Float(prng.borrow_mut().f64())
+            }),
+            purity: Purity::Impure,
+        }))
     });
 }