Move the storage of MessageContentModels to the room

Move the storage of MessageContentModels to the room in the same manner as memeber objects to prevent duplication but mainly to make the system easier to maintain going forward with things like threads for example. This requires the creation of a MessageContentFilterModel as the same model may be used in multiple places, sometimes with the author showning sometimes not.

src/models/messagecontentfiltermodel.h

@@ -0,0 +1,43 @@
+// SPDX-FileCopyrightText: 2025 James Graham <james.h.graham@protonmail.com>
+// SPDX-License-Identifier: GPL-2.0-only OR GPL-3.0-only OR LicenseRef-KDE-Accepted-GPL
+
+#pragma once
+
+#include <QQmlEngine>
+#include <QSortFilterProxyModel>
+
+/**
+ * @class MessageContentFilterModel
+ *
+ * This model filters a message's contents.
+ */
+class MessageContentFilterModel : public QSortFilterProxyModel
+{
+    Q_OBJECT
+    QML_ELEMENT
+
+    /**
+     * @brief Whether the author component should be shown.
+     */
+    Q_PROPERTY(bool showAuthor READ showAuthor WRITE setShowAuthor NOTIFY showAuthorChanged)
+
+public:
+    explicit MessageContentFilterModel(QObject *parent = nullptr);
+
+    bool showAuthor() const;
+    void setShowAuthor(bool showAuthor);
+
+Q_SIGNALS:
+    void showAuthorChanged();
+
+protected:
+    /**
+     * @brief Whether a row should be shown out or not.
+     *
+     * @sa QSortFilterProxyModel::filterAcceptsRow
+     */
+    [[nodiscard]] bool filterAcceptsRow(int source_row, const QModelIndex &source_parent) const override;
+
+private:
+    bool m_showAuthor = true;
+};