feat(etl): implement ColumnRenameTransformer

Add transformer for renaming columns in the data stream during ETL.
Supports case-insensitive column name matching and multiple renames.

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

@@ -0,0 +1,51 @@
+using System.Data;
+
+namespace JdeScoping.DataSync.Etl.Transformers;
+
+/// <summary>
+/// A data transformer that renames specified columns in the data stream.
+/// Columns are matched by name (case-insensitive).
+/// </summary>
+public class ColumnRenameTransformer : DataTransformerBase
+{
+    private readonly Dictionary<string, string> _renames;
+    private string[]? _outputNames;
+    private Dictionary<string, int>? _nameToOrdinal;
+
+    /// <inheritdoc />
+    public override string TransformerName => $"RenameColumns:{_renames.Count}";
+
+    /// <summary>
+    /// Creates a new ColumnRenameTransformer that renames the specified columns.
+    /// </summary>
+    /// <param name="renames">Tuples of (OldName, NewName) for columns to rename (case-insensitive matching).</param>
+    public ColumnRenameTransformer(params (string OldName, string NewName)[] renames)
+    {
+        ArgumentNullException.ThrowIfNull(renames);
+        _renames = renames.ToDictionary(r => r.OldName, r => r.NewName, StringComparer.OrdinalIgnoreCase);
+    }
+
+    /// <inheritdoc />
+    protected override void OnInitialize(IDataReader source)
+    {
+        _outputNames = new string[source.FieldCount];
+        _nameToOrdinal = new Dictionary<string, int>(StringComparer.OrdinalIgnoreCase);
+        for (int i = 0; i < source.FieldCount; i++)
+        {
+            var originalName = source.GetName(i);
+            var outputName = _renames.TryGetValue(originalName, out var newName) ? newName : originalName;
+            _outputNames[i] = outputName;
+            _nameToOrdinal[outputName] = i;
+        }
+    }
+
+    /// <inheritdoc />
+    public override string GetName(int ordinal, IDataReader source) => _outputNames![ordinal];
+
+    /// <inheritdoc />
+    public override int GetOrdinal(string name, IDataReader source)
+    {
+        if (_nameToOrdinal!.TryGetValue(name, out var ordinal)) return ordinal;
+        throw new IndexOutOfRangeException($"Column '{name}' not found.");
+    }
+}

NEW/tests/JdeScoping.DataSync.Tests/Etl/Transformers/ColumnRenameTransformerTests.cs

@@ -0,0 +1,69 @@
+using System.Data;
+using JdeScoping.DataSync.Etl.Transformers;
+using NSubstitute;
+
+namespace JdeScoping.DataSync.Tests.Etl.Transformers;
+
+public class ColumnRenameTransformerTests
+{
+    [Fact]
+    public void GetName_ReturnsRenamedColumn()
+    {
+        var source = CreateMockReader(new[] { "OldName", "Other" });
+        var transformer = new ColumnRenameTransformer(("OldName", "NewName"));
+        var reader = transformer.Transform(source);
+        Assert.Equal("NewName", reader.GetName(0));
+        Assert.Equal("Other", reader.GetName(1));
+    }
+
+    [Fact]
+    public void GetOrdinal_FindsByNewName()
+    {
+        var source = CreateMockReader(new[] { "OldName", "Other" });
+        var transformer = new ColumnRenameTransformer(("OldName", "NewName"));
+        var reader = transformer.Transform(source);
+        Assert.Equal(0, reader.GetOrdinal("NewName"));
+    }
+
+    [Fact]
+    public void GetOrdinal_OldName_ThrowsIndexOutOfRange()
+    {
+        var source = CreateMockReader(new[] { "OldName", "Other" });
+        var transformer = new ColumnRenameTransformer(("OldName", "NewName"));
+        var reader = transformer.Transform(source);
+        Assert.Throws<IndexOutOfRangeException>(() => reader.GetOrdinal("OldName"));
+    }
+
+    [Fact]
+    public void FieldCount_Unchanged()
+    {
+        var source = CreateMockReader(new[] { "OldName", "Other" });
+        var transformer = new ColumnRenameTransformer(("OldName", "NewName"));
+        var reader = transformer.Transform(source);
+        Assert.Equal(2, reader.FieldCount);
+    }
+
+    [Fact]
+    public void MultipleRenames_AllApplied()
+    {
+        var source = CreateMockReader(new[] { "A", "B", "C" });
+        var transformer = new ColumnRenameTransformer(("A", "Alpha"), ("C", "Charlie"));
+        var reader = transformer.Transform(source);
+        Assert.Equal("Alpha", reader.GetName(0));
+        Assert.Equal("B", reader.GetName(1));
+        Assert.Equal("Charlie", reader.GetName(2));
+    }
+
+    private static IDataReader CreateMockReader(string[] columns)
+    {
+        var reader = Substitute.For<IDataReader>();
+        reader.FieldCount.Returns(columns.Length);
+        for (int i = 0; i < columns.Length; i++)
+        {
+            var index = i;
+            reader.GetName(index).Returns(columns[index]);
+            reader.GetOrdinal(columns[index]).Returns(index);
+        }
+        return reader;
+    }
+}