Refactor namespace and add System.Linq import

Removed conditional compilation around the namespace in DbRepository.cs, making it always use standard braces. Added System.Linq using directive to support LINQ operations.

DigitalData.Core.Infrastructure/DbRepository.cs

@@ -13,12 +13,7 @@ using System.Threading.Tasks;
 #endif
 
 namespace DigitalData.Core.Infrastructure
-#if NET
-    ;
-#elif NETFRAMEWORK
-    {
-#endif
-
+{
     public class DbRepository<TDbContext> where TDbContext : DbContext
     {
         protected internal readonly TDbContext Context;
@@ -155,6 +150,4 @@ namespace DigitalData.Core.Infrastructure
         public virtual IQueryable<TEntity> ReadOnly() => Entities.AsNoTracking();
         #endregion
     }
-#if NETFRAMEWORK
-    }
-#endif
+}