feat: ETLng loader basics (#1808)

For #1597

src/util/async/AnyStopToken.hpp

@@ -24,6 +24,7 @@
 
 #include <boost/asio/spawn.hpp>
 
+#include <chrono>
 #include <memory>
 #include <type_traits>
 #include <utility>

src/util/async/context/impl/Cancellation.hpp

@@ -19,8 +19,10 @@
 
 #pragma once
 
+#include <boost/asio/associated_executor.hpp>
 #include <boost/asio/post.hpp>
 #include <boost/asio/spawn.hpp>
+#include <boost/asio/steady_timer.hpp>
 
 #include <atomic>
 #include <memory>