Fix AccountDeleteInPostPlugin being auto-registered across all tests

The plugin extended Plugin directly, causing it to be discovered and
registered by the base type scanner for every test that updated an
account, deleting records in unrelated tests.

Fix:
- Change AccountDeleteInPostPlugin to extend TestPlugin (an intermediate
  abstract class) instead of Plugin directly. The scanner uses
  t.BaseType == basePluginType so transitively-inherited plugins are
  not auto-discovered.
- Add missing #pragma warning disable CS0618 around RegisterPluginStep
  (consistent with other test plugins, also fixes CodeFactor warning).
- Simplify test assertions to use already-imported QueryExpression types
  instead of fully-qualified names.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: contextduck

tests/TestPluginAssembly365/Plugins/AccountDeleteInPostPlugin.cs

@@ -2,20 +2,23 @@
 namespace DG.Some.Namespace {
     using System;
     using DG.XrmFramework.BusinessDomain.ServiceContext;
+    using TestPluginAssembly365.Plugins.SyncAsyncTest;
     using XrmPluginCore;
     using XrmPluginCore.Enums;
 
     /// <summary>
     /// Test plugin that deletes the target account in a post-Update operation.
     /// Used to verify that XrmMockup handles record deletion inside a post-operation plugin gracefully.
     /// </summary>
-    public class AccountDeleteInPostPlugin : Plugin {
+    public class AccountDeleteInPostPlugin : TestPlugin {
 
         public AccountDeleteInPostPlugin() {
+#pragma warning disable CS0618 // Type or member is obsolete - disabled for testing purposes
             RegisterPluginStep<Account>(
                 EventOperation.Update,
                 ExecutionStage.PostOperation,
                 Execute);
+#pragma warning restore CS0618 // Type or member is obsolete
         }
 
         protected void Execute(LocalPluginContext localContext) {

tests/XrmMockup365Test/TestPlugins.cs

@@ -236,13 +236,13 @@ public void TestDeleteTargetInPostUpdatePlugin()
 
             // Verify the account was actually deleted by the plugin
             var retrieved = orgAdminService.RetrieveMultiple(
-                new Microsoft.Xrm.Sdk.Query.QueryExpression(Account.EntityLogicalName)
+                new QueryExpression(Account.EntityLogicalName)
                 {
-                    Criteria = new Microsoft.Xrm.Sdk.Query.FilterExpression
+                    Criteria = new FilterExpression
                     {
                         Conditions =
                         {
-                            new Microsoft.Xrm.Sdk.Query.ConditionExpression("accountid", Microsoft.Xrm.Sdk.Query.ConditionOperator.Equal, account.Id)
+                            new ConditionExpression("accountid", ConditionOperator.Equal, account.Id)
                         }
                     }
                 });