feat(etl): add binary method overrides to DataTransformerBase

Add virtual methods to DataTransformerBase for GetBytes, GetChars,
GetData, and GetDataTypeName that properly handle computed columns
by throwing NotSupportedException when MapOrdinal returns -1.

Update TransformingDataReader to delegate these methods to the
transformer instead of directly to the source reader.

NEW/src/JdeScoping.DataSync/Etl/Transformers/DataTransformerBase.cs

@@ -71,4 +71,58 @@ public abstract class DataTransformerBase : IDataTransformer
     /// <param name="source">The source data reader.</param>
     /// <returns>The corresponding source ordinal, or -1 for computed columns.</returns>
     public virtual int MapOrdinal(int transformedOrdinal, IDataReader source) => transformedOrdinal;
+
+    /// <summary>
+    /// Gets bytes from a field at the specified ordinal.
+    /// Throws NotSupportedException for computed columns (where MapOrdinal returns -1).
+    /// </summary>
+    public virtual long GetBytes(int ordinal, long fieldOffset, byte[]? buffer,
+        int bufferOffset, int length, IDataReader source)
+    {
+        var sourceOrdinal = MapOrdinal(ordinal, source);
+        if (sourceOrdinal < 0)
+            throw new NotSupportedException(
+                $"GetBytes not supported for computed column at ordinal {ordinal}.");
+        return source.GetBytes(sourceOrdinal, fieldOffset, buffer, bufferOffset, length);
+    }
+
+    /// <summary>
+    /// Gets characters from a field at the specified ordinal.
+    /// Throws NotSupportedException for computed columns (where MapOrdinal returns -1).
+    /// </summary>
+    public virtual long GetChars(int ordinal, long fieldOffset, char[]? buffer,
+        int bufferOffset, int length, IDataReader source)
+    {
+        var sourceOrdinal = MapOrdinal(ordinal, source);
+        if (sourceOrdinal < 0)
+            throw new NotSupportedException(
+                $"GetChars not supported for computed column at ordinal {ordinal}.");
+        return source.GetChars(sourceOrdinal, fieldOffset, buffer, bufferOffset, length);
+    }
+
+    /// <summary>
+    /// Gets nested data reader for a field at the specified ordinal.
+    /// Throws NotSupportedException for computed columns (where MapOrdinal returns -1).
+    /// </summary>
+    public virtual IDataReader GetData(int ordinal, IDataReader source)
+    {
+        var sourceOrdinal = MapOrdinal(ordinal, source);
+        if (sourceOrdinal < 0)
+            throw new NotSupportedException(
+                $"GetData not supported for computed column at ordinal {ordinal}.");
+        return source.GetData(sourceOrdinal);
+    }
+
+    /// <summary>
+    /// Gets the data type name for a field at the specified ordinal.
+    /// Throws NotSupportedException for computed columns (where MapOrdinal returns -1).
+    /// </summary>
+    public virtual string GetDataTypeName(int ordinal, IDataReader source)
+    {
+        var sourceOrdinal = MapOrdinal(ordinal, source);
+        if (sourceOrdinal < 0)
+            throw new NotSupportedException(
+                $"GetDataTypeName not supported for computed column at ordinal {ordinal}.");
+        return source.GetDataTypeName(sourceOrdinal);
+    }
 }

NEW/src/JdeScoping.DataSync/Etl/Transformers/TransformingDataReader.cs

@@ -50,8 +50,8 @@ internal sealed class TransformingDataReader : IDataReader
     public long GetInt64(int i) => (long)GetValue(i);
     public string GetString(int i) => (string)GetValue(i);
 
-    // Schema and bulk data access - delegated to source
-    public string GetDataTypeName(int i) => _source.GetDataTypeName(i);
+    // Schema and bulk data access - delegated to transformer
+    public string GetDataTypeName(int i) => _transformer.GetDataTypeName(i, _source);
 
     public int GetValues(object[] values)
     {
@@ -62,12 +62,12 @@ internal sealed class TransformingDataReader : IDataReader
     }
 
     public long GetBytes(int i, long fieldOffset, byte[]? buffer, int bufferoffset, int length)
-        => _source.GetBytes(i, fieldOffset, buffer, bufferoffset, length);
+        => _transformer.GetBytes(i, fieldOffset, buffer, bufferoffset, length, _source);
 
     public long GetChars(int i, long fieldoffset, char[]? buffer, int bufferoffset, int length)
-        => _source.GetChars(i, fieldoffset, buffer, bufferoffset, length);
+        => _transformer.GetChars(i, fieldoffset, buffer, bufferoffset, length, _source);
 
-    public IDataReader GetData(int i) => _source.GetData(i);
+    public IDataReader GetData(int i) => _transformer.GetData(i, _source);
 
     public DataTable? GetSchemaTable() => _source.GetSchemaTable();
 }