feat(05-01): make helper methods internal and add unit tests

- Changed IsThrottleException to internal static in ExecuteQueryRetryHelper
- Changed BuildPagedViewXml to internal static in SharePointPaginationHelper
- Created ExecuteQueryRetryHelperTests: 5 tests (throttle true x3, non-throttle false, nested false)
- Created SharePointPaginationHelperTests: 5 tests (null, empty, whitespace, replace, append)

SharepointToolbox.Tests/Helpers/SharePointPaginationHelperTests.cs

@@ -0,0 +1,49 @@
+using SharepointToolbox.Core.Helpers;
+
+namespace SharepointToolbox.Tests.Helpers;
+
+[Trait("Category", "Unit")]
+public class SharePointPaginationHelperTests
+{
+    [Fact]
+    public void BuildPagedViewXml_NullInput_ReturnsViewWithRowLimit()
+    {
+        var result = SharePointPaginationHelper.BuildPagedViewXml(null, 2000);
+        Assert.Equal("<View><RowLimit>2000</RowLimit></View>", result);
+    }
+
+    [Fact]
+    public void BuildPagedViewXml_EmptyString_ReturnsViewWithRowLimit()
+    {
+        var result = SharePointPaginationHelper.BuildPagedViewXml("", 2000);
+        Assert.Equal("<View><RowLimit>2000</RowLimit></View>", result);
+    }
+
+    [Fact]
+    public void BuildPagedViewXml_WhitespaceOnly_ReturnsViewWithRowLimit()
+    {
+        var result = SharePointPaginationHelper.BuildPagedViewXml("   ", 2000);
+        Assert.Equal("<View><RowLimit>2000</RowLimit></View>", result);
+    }
+
+    [Fact]
+    public void BuildPagedViewXml_ExistingRowLimit_Replaces()
+    {
+        var input = "<View><RowLimit>100</RowLimit></View>";
+        var result = SharePointPaginationHelper.BuildPagedViewXml(input, 2000);
+        Assert.Equal("<View><RowLimit>2000</RowLimit></View>", result);
+    }
+
+    [Fact]
+    public void BuildPagedViewXml_NoRowLimit_AppendsBeforeClosingView()
+    {
+        var input = "<View><Query><OrderBy><FieldRef Name='Title'/></OrderBy></Query></View>";
+        var result = SharePointPaginationHelper.BuildPagedViewXml(input, 2000);
+        Assert.Contains("<RowLimit>2000</RowLimit>", result);
+        Assert.EndsWith("</View>", result);
+        // Ensure RowLimit is inserted before the closing </View>
+        var rowLimitIndex = result.IndexOf("<RowLimit>2000</RowLimit>", StringComparison.Ordinal);
+        var closingViewIndex = result.LastIndexOf("</View>", StringComparison.Ordinal);
+        Assert.True(rowLimitIndex < closingViewIndex, "RowLimit should appear before </View>");
+    }
+}