.NET: Add unit tests for EditTableV2Executor (#3773)

* Initial plan

* Add comprehensive unit tests for EditTableV2Executor

- Test AddItemOperation with record and scalar values
- Test ClearItemsOperation
- Test RemoveItemOperation
- Test TakeLastItemOperation (with items and empty table)
- Test TakeFirstItemOperation (with items and empty table)
- Test error cases (null ItemsVariable, non-table variable)
- Include ExecuteTestAsync and CreateModel helper methods
- All 10 tests passing

Co-authored-by: crickman <66376200+crickman@users.noreply.github.com>

* Add comprehensive unit tests for EditTableV2Executor - complete with 100% coverage

- Added 13 comprehensive tests covering all code paths
- Test AddItemOperation with record and scalar values
- Test ClearItemsOperation
- Test RemoveItemOperation (including non-table value case)
- Test TakeLastItemOperation (with items and empty table)
- Test TakeFirstItemOperation (with items and empty table)
- Test error cases (null ItemsVariable, non-table variable, null operation values)
- Include ExecuteTestAsync and CreateModel helper methods
- 100% line and branch coverage achieved

Co-authored-by: crickman <66376200+crickman@users.noreply.github.com>

* Update tests / refine product code

* Checkpoint

* Updated

* Update dotnet/tests/Microsoft.Agents.AI.Workflows.Declarative.UnitTests/ObjectModel/SetTextVariableExecutorTest.cs

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Address code review feedback

- Fix typo: rename metadataExpresssion to metadataExpression
- Fix test name in AddMessageWithMetadataAsync (was using wrong test name)
- Fix test name in ClearGlobalScopeAsync (was using wrong test name)
- Remove pre-population in SetTextVariableExecutorTest that made tests ineffective
- Use explicit .Where() filter in SetMultipleVariablesExecutorTest foreach loop

Co-authored-by: crickman <66376200+crickman@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: crickman <66376200+crickman@users.noreply.github.com>
Co-authored-by: Chris Rickman <crickman@microsoft.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

dotnet/src/Microsoft.Agents.AI.Workflows.Declarative/ObjectModel/ClearAllVariablesExecutor.cs

@@ -23,7 +23,7 @@ internal sealed class ClearAllVariablesExecutor(ClearAllVariables model, Workflo
             VariablesToClear.ConversationScopedVariables => WorkflowFormulaState.DefaultScopeName,
             VariablesToClear.ConversationHistory => null,
             VariablesToClear.UserScopedVariables => null,
-            _ => null
+            _ => null,
         };
 
         if (scope is not null)