Make PropertyIdentifierAndOffset internal

I think it should be treated as an implementation detail of the (already internal) PropertySet/PropertySetStream

OpenMcdf.Ole/PropertyIdentifierAndOffset.cs

@@ -1,6 +1,6 @@
 namespace OpenMcdf.Ole;
 
-public class PropertyIdentifierAndOffset : IBinarySerializable
+internal sealed class PropertyIdentifierAndOffset : IBinarySerializable
 {
     public uint PropertyIdentifier { get; set; }
     public uint Offset { get; set; }