[development] fixed ambiguous 'byte' type MSVC build error (#7184)

- fully quality 'byte' type in AZStd::span
- remove unnecessary 'using namespace AZStd;' statement from AssetCatalog tests

Signed-off-by: AMZN-ScottR <24445312+AMZN-ScottR@users.noreply.github.com>

Code/Framework/AzFramework/Tests/AssetCatalog.cpp

@@ -34,7 +34,6 @@
 
 #include "AZTestShared/Utils/Utils.h"
 
-using namespace AZStd;
 using namespace AZ::Data;
 
 namespace UnitTest