feat: add pow(_) primitive to Num class for exponentiation

Implement the `num_pow` primitive that wraps C's `pow()` function, enabling
exponentiation on Num instances via the `pow(_)` method. Register the new
primitive in `wrenInitializeCore` and add a test file verifying basic cases:
2^4=16, 2^10=1024, and 1^0=1.

src/vm/wren_core.c

@@ -644,6 +644,11 @@ DEF_PRIMITIVE(num_atan2)
   RETURN_NUM(atan2(AS_NUM(args[0]), AS_NUM(args[1])));
 }
 
+DEF_PRIMITIVE(num_pow)
+{
+  RETURN_NUM(pow(AS_NUM(args[0]), AS_NUM(args[1])));
+}
+
 DEF_PRIMITIVE(num_fraction)
 {
   double dummy;
@@ -1272,6 +1277,7 @@ void wrenInitializeCore(WrenVM* vm)
   PRIMITIVE(vm->numClass, "..(_)", num_dotDot);
   PRIMITIVE(vm->numClass, "...(_)", num_dotDotDot);
   PRIMITIVE(vm->numClass, "atan(_)", num_atan2);
+  PRIMITIVE(vm->numClass, "pow(_)", num_pow);
   PRIMITIVE(vm->numClass, "fraction", num_fraction);
   PRIMITIVE(vm->numClass, "isInfinity", num_isInfinity);
   PRIMITIVE(vm->numClass, "isInteger", num_isInteger);

test/core/number/pow.wren

@@ -0,0 +1,4 @@
+System.print(2.pow(4))     // expect: 16
+System.print(2.pow(10))    // expect: 1024
+
+System.print(1.pow(0))     // expect: 1