Add ColumnNames property to EntityBaseOptions

Added a new ColumnNames property that exposes the column names from the ColumnMappings dictionary as an IEnumerable<string> in the EntityBaseOptions record. This provides convenient access to mapped column names alongside existing property name access.

src/ReC.Infrastructure/Options/Shared/EntityBaseOptions.cs

@@ -8,6 +8,8 @@ public record EntityBaseOptions()
 
     public IEnumerable<string> PropertyNames => ColumnMappings.Select(col => col.Key);
 
+    public IEnumerable<string> ColumnNames => ColumnMappings.Select(col => col.Value);
+
     public void EnsureProperties(IEnumerable<string> propertyNames)
     {
         var missingProperties = propertyNames.Except(PropertyNames).ToList();