Reduce bloat due to statics

Avoid disseminating every compile unit including Message.h with TransportNames and
TransportTypes and the associated unordered_map helper methods (e.g.
murmur_hash).

fairmq/TransportEnum.h

@@ -0,0 +1,22 @@
+/********************************************************************************
+ * Copyright (C) 2014-2025 GSI Helmholtzzentrum fuer Schwerionenforschung GmbH  *
+ *                                                                              *
+ *              This software is distributed under the terms of the             *
+ *              GNU Lesser General Public Licence (LGPL) version 3,             *
+ *                  copied verbatim in the file "LICENSE"                       *
+ ********************************************************************************/
+
+#ifndef FAIR_MQ_TRANSPORTENUMS_H
+#define FAIR_MQ_TRANSPORTENUMS_H
+
+namespace fair::mq {
+
+enum class Transport {
+    DEFAULT,
+    ZMQ,
+    SHM
+};
+
+}
+
+#endif // FAIR_MQ_TRANSPORTENUMS_H