moved column and table class from namespace sql to query

include/matador/sql/record.hpp

@@ -8,8 +8,6 @@
 
 namespace matador::sql {
 
-class column;
-
 class record final {
 private:
   using field_ref = std::reference_wrapper<field>;
@@ -41,11 +39,11 @@ public:
 
   [[nodiscard]] const std::vector<field_ref>& columns() const;
 
-  [[nodiscard]] const field& at(const sql::column &col) const;
+  [[nodiscard]] const field& at(const std::string &name) const;
   [[nodiscard]] const field& at(size_t index) const;
   template<class Type>
-  std::optional<Type> at(const column &col) const {
-    return at(col).as<Type>();
+  std::optional<Type> at(const std::string &name) const {
+    return at(name).as<Type>();
   }
   template<class Type>
   std::optional<Type> at(const size_t index) const {