RootStorageSvc+RootAuxDynIO: Move RPageSource from Detail to Internal namespace

This MR should fix the compilation errors in the main--dev3LCG nightly and is a stopgap solution until !68810 (closed) is ironed out.

cc: @gemmeren @mnowak

Database/APR/RootStorageSvc/src/RNTupleContainer.h

@@ -25,12 +25,14 @@ class IRootAuxDynWriter;
 namespace SG { class IAuxStoreIO; }
 namespace RootAuxDynIO { class IRNTupleWriter; }
 namespace ROOT { namespace Experimental {
+#if ROOT_VERSION_CODE < ROOT_VERSION( 6, 31, 0 )
   namespace Detail {
     class RPageSource;
-#if ROOT_VERSION_CODE < ROOT_VERSION( 6, 31, 0 )
     class RFieldBase;
   }
 #else
+  namespace Internal {
+    class RPageSource;
   }
   class RFieldBase;
 #endif
@@ -43,10 +45,11 @@ namespace pool {
 
 #if ROOT_VERSION_CODE >= ROOT_VERSION( 6, 31, 0 )
 using ROOT::Experimental::RFieldBase;
+using ROOT::Experimental::Internal::RPageSource;
 #else
 using ROOT::Experimental::Detail::RFieldBase;
-#endif
 using ROOT::Experimental::Detail::RPageSource;
+#endif
 
 // Forward declaration
 class DbColumn;