feat: add wrenGetSlotListSize and wrenGetSlotListValue API functions for list introspection

Add two new C API functions to the Wren VM that allow foreign methods to query the size of a list stored in a slot and retrieve individual values from it by index. The implementation validates the slot holds a list, extracts the internal ValueBuffer, and returns the count or a captured WrenValue respectively. Corresponding test bindings (getListSize, getListValue) and Wren test cases are included to verify the new functionality.

src/include/wren.h

@@ -359,6 +359,12 @@ double wrenGetSlotDouble(WrenVM* vm, int slot);
 // foreign class.
 void* wrenGetSlotForeign(WrenVM* vm, int slot);
 
+// Returns the size of the list stored in [slot].
+int wrenGetSlotListSize(WrenVM* vm, int slot);
+
+// Reads a value from the list in [slot].
+WrenValue* wrenGetSlotListValue(WrenVM* vm, int slot, int index);
+
 // Reads a string from [slot].
 //
 // The memory for the returned string is owned by Wren. You can inspect it