Improve search experience somewhat

So I noticed that searching for messages feels "buggy". I dove into the
code and gave it a pretty nice refresh, I know you'll like it once you
try it!

Some of the issues I noticed and are now fixed:
* The search doesn't clear immediately when you clear the text box, it's
delayed like everything else. This also has the knock-on effect of
starting random network requests.
* If you now press the search button (either with a mouse, pen, etc. or
by the keyboard) the search delay timer was still running.
* The "nothing is here" placeholder message appears when the search
timer is running, making you think no messages were found.

These changes also help other places where SearchPage is used, not just
message search.

src/libneochat/qml/SearchPage.qml

@@ -112,7 +112,7 @@ Kirigami.ScrollablePage {
      * @brief Force the search to be updated if the model has a valid search function.
      */
     function updateSearch() {
-        searchTimer.restart();
+        root.model.search();
     }
 
     header: QQC2.Control {
@@ -142,10 +142,13 @@ Kirigami.ScrollablePage {
                 Layout.fillWidth: true
                 Keys.onEnterPressed: searchButton.clicked()
                 Keys.onReturnPressed: searchButton.clicked()
-                onTextChanged: {
-                    searchTimer.restart();
-                    if (root.model) {
-                        root.model.searchText = text;
+                onTextChanged: root.model.searchText = text
+                onAccepted: {
+                    // If the text is empty, call the search model immediately because it will early-return.
+                    if (root.model.searchText.length === 0) {
+                        root.model.search();
+                    } else {
+                        searchTimer.restart();
                     }
                 }
             }
@@ -158,6 +161,7 @@ Kirigami.ScrollablePage {
 
                 onClicked: {
                     if (typeof root.model.search === 'function') {
+                        searchTimer.stop();
                         root.model.search();
                     }
                 }
@@ -197,7 +201,7 @@ Kirigami.ScrollablePage {
             id: noResultMessage
             icon.name: "search"
             anchors.centerIn: parent
-            visible: searchField.text.length > 0 && listView.count === 0 && !root.model.searching && customPlaceholder.text.length === 0
+            visible: searchField.text.length > 0 && listView.count === 0 && (!root.model.searching && !searchTimer.running) && customPlaceholder.text.length === 0
             helpfulAction: root.noResultHelpfulAction
         }
 
@@ -210,7 +214,7 @@ Kirigami.ScrollablePage {
 
         Kirigami.LoadingPlaceholder {
             anchors.centerIn: parent
-            visible: searchField.text.length > 0 && listView.count === 0 && root.model.searching && customPlaceholder.text.length === 0
+            visible: searchField.text.length > 0 && listView.count === 0 && (root.model.searching || searchTimer.running) && customPlaceholder.text.length === 0
         }
 
         Keys.onUpPressed: {

src/timeline/models/searchmodel.cpp

@@ -26,12 +26,24 @@ void SearchModel::setSearchText(const QString &searchText)
 void SearchModel::search()
 {
     Q_ASSERT(m_room);
-    setSearching(true);
+
     if (m_job) {
         m_job->abandon();
         m_job = nullptr;
     }
 
+    // early-return case: the user sets the text to nothing, and we simply clear the results
+    if (m_searchText.isEmpty()) {
+        clearEventObjects();
+
+        beginResetModel();
+        m_result = std::nullopt;
+        endResetModel();
+        return;
+    }
+
+    setSearching(true);
+
     RoomEventFilter filter;
     filter.unreadThreadNotifications = std::nullopt;
     filter.lazyLoadMembers = true;
@@ -48,7 +60,6 @@ void SearchModel::search()
         .eventContext = SearchJob::IncludeEventContext{3, 3, true},
         .includeState = false,
         .groupings = std::nullopt,
-
     };
 
     auto job = m_room->connection()->callApi<SearchJob>(SearchJob::Categories{criteria});