insert query builder insert step improvements

source/orm/sql/connection_pool.cpp

@@ -9,7 +9,7 @@ identifiable_connection::identifiable_connection(const size_t id, connection con
 , conn(std::move(conn)){}
 
 connection_ptr::~connection_ptr() {
-  pool_->release(connection_);
+  release();
 }
 
 connection_ptr::connection_ptr(identifiable_connection* c, connection_pool* pool)
@@ -53,6 +53,10 @@ bool connection_ptr::valid() const {
   return connection_ != nullptr;
 }
 
+void connection_ptr::release() const {
+  pool_->release(connection_);
+}
+
 connection_pool::connection_pool(const std::string& dns, const size_t count)
 : connection_pool(dns, count, [](const connection_info &info) { return connection{info}; })
 {}