Revert "refactor: move tr_torrent callbacks to tr_session (#3003)" (#3104)

This reverts commit 27fbfd8da6.

Fixes #3088.

gtk/Session.cc

@@ -813,8 +813,8 @@ Session::Session(tr_session* session)
 Session::~Session() = default;
 
 Session::Impl::Impl(Session& core, tr_session* session)
-    : core_{ core }
-    , session_{ session }
+    : core_(core)
+    , session_(session)
 {
     raw_model_ = Gtk::ListStore::create(torrent_cols);
     sorted_model_ = Gtk::TreeModelSort::create(raw_model_);
@@ -828,16 +828,6 @@ Session::Impl::Impl(Session& core, tr_session* session)
     on_pref_changed(TR_KEY_peer_limit_global);
     on_pref_changed(TR_KEY_inhibit_desktop_hibernation);
     signal_prefs_changed.connect([this](auto key) { on_pref_changed(key); });
-
-    tr_sessionSetMetadataCallback(
-        session_,
-        [](auto* tor2, gpointer impl) { static_cast<Impl*>(impl)->on_torrent_metadata_changed(tor2); },
-        this);
-    tr_sessionSetCompletenessCallback(
-        session_,
-        [](auto* tor2, auto completeness, bool was_running, gpointer impl)
-        { static_cast<Impl*>(impl)->on_torrent_completeness_changed(tor2, completeness, was_running); },
-        this);
 }
 
 tr_session* Session::close()
@@ -996,6 +986,16 @@ void Session::Impl::add_torrent(tr_torrent* tor, bool do_notify)
         {
             gtr_notify_torrent_added(get_core_ptr(), tr_torrentId(tor));
         }
+
+        tr_torrentSetMetadataCallback(
+            tor,
+            [](auto* tor2, gpointer impl) { static_cast<Impl*>(impl)->on_torrent_metadata_changed(tor2); },
+            this);
+        tr_torrentSetCompletenessCallback(
+            tor,
+            [](auto* tor2, auto completeness, bool was_running, gpointer impl)
+            { static_cast<Impl*>(impl)->on_torrent_completeness_changed(tor2, completeness, was_running); },
+            this);
     }
 }