CActor: Make Render() a non-const function

A few implementations of Render() contain const-casts nested within its
their call hierarchy to get around the fact that this function is marked
const. We can just make the member function non-const to allow removal
of these casts in follow up changes.

Runtime/World/CEffect.hpp

@@ -9,7 +9,7 @@ public:
   CEffect(TUniqueId uid, const CEntityInfo& info, bool active, std::string_view name, const zeus::CTransform& xf);
 
   void AddToRenderer(const zeus::CFrustum&, CStateManager&) override {}
-  void Render(const CStateManager&) const override {}
+  void Render(CStateManager&) override {}
 };
 
 } // namespace urde