integrated object cache into session and added message bus to object_cache and update tests

include/matador/object/object_ptr.hpp

@@ -57,6 +57,8 @@ public:
   void reset() { proxy_.reset(); }
   void reset(const std::shared_ptr<object_proxy<Type>>& proxy) { proxy_ = proxy; }
 
+  [[nodiscard]] std::shared_ptr<object_proxy<Type>> proxy() const { return proxy_; }
+
   operator bool() const { return valid(); }
   [[nodiscard]] bool valid() const { return proxy_ != nullptr && !proxy_->empty(); }