[CardInfo] use QString QHash instead of QVariantHash for properties (#7063)

* [CardInfo] use QString QHash instead of QVariantHash for properties

* bump CACHE_VERSION

* cleanups

libcockatrice_card/libcockatrice/card/database/parser/cockatrice_xml_4.h

@@ -19,7 +19,7 @@ inline Q_LOGGING_CATEGORY(CockatriceXml4Log, "cockatrice_xml.xml_4_parser");
  * making the parser more extensible and schema-compliant.
  *
  * @note Differences from v3:
- * - Card properties are stored in <prop> blocks as a QVariantHash.
+ * - Card properties are stored in <prop> blocks as a QHash<QString, QString>.
  * - Sets can include a <priority> element.
  * - Supports user preferences via ICardPreferenceProvider (e.g., skipping rebalanced cards).
  * - Related cards support persistent relations and multiple attach types (e.g., transform).
@@ -70,9 +70,9 @@ private:
     /**
      * @brief Loads a generic <prop> block from a <card> element.
      * @param xml The open QXmlStreamReader positioned at a <prop> element.
-     * @return A QVariantHash mapping property names to values.
+     * @return A QHash<QString, QString> mapping property names to values.
      */
-    QVariantHash loadCardPropertiesFromXml(QXmlStreamReader &xml);
+    QHash<QString, QString> loadCardPropertiesFromXml(QXmlStreamReader &xml);
 
     /**
      * @brief Load all <card> elements from the XML stream.