use ADL-findable unpack function to unpack

Event/EventPacker/src/component/BufferUnpackerBaseAlg.cpp

@@ -14,8 +14,10 @@
 using namespace LHCb::Packers::Traits;
 using namespace LHCb::Hlt::PackedData;
 
-namespace {
+using namespace LHCb::Packers::Traits;
+using namespace LHCb::Hlt::PackedData;
 
+namespace {
 #if 0
   class PTMap {
     // TODO: keep track of the names of all transient types for this packed type