chore(toolkit-lib): remove duplicate test helpers (#507)

This PR removes duplicate test helper functions in the toolkit-lib
package to improve code maintainability and reduce redundancy.

---
By submitting this pull request, I confirm that my contribution is made
under the terms of the Apache-2.0 license

Author: mrgrain

packages/@aws-cdk/toolkit-lib/lib/api/io/private/testing/fake-io-host.ts

@@ -2,10 +2,10 @@ import { GetParameterCommand } from '@aws-sdk/client-ssm';
 import { ToolkitInfo } from '../../../lib/api';
 import { Context } from '../../../lib/api/context';
 import { EnvironmentResourcesRegistry } from '../../../lib/api/environment';
-import { FakeIoHost } from '../../../lib/api/io/private/testing/fake-io-host';
 import { Notices } from '../../../lib/api/notices';
 import { CachedDataSource } from '../../../lib/api/notices/cached-data-source';
 import { NoticesFilter } from '../../../lib/api/notices/filter';
+import { FakeIoHost } from '../../_helpers/fake-io-host';
 import { MockSdk, mockBootstrapStack, mockSSMClient } from '../../_helpers/mock-sdk';
 import { TestIoHost } from '../../_helpers/test-io-host';
 import { MockToolkitInfo } from '../_helpers/mock-toolkitinfo';

packages/@aws-cdk/toolkit-lib/lib/api/io/private/testing/index.ts

@@ -1,7 +1,7 @@
 import type { CredentialProviderSource, SDKv3CompatibleCredentials } from '@aws-cdk/cli-plugin-contract';
 import { CredentialPlugins, credentialsAboutToExpire } from '../../../lib/api/aws-auth/private';
-import { TestIoHost } from '../../../lib/api/io/private/testing';
 import { Mode, PluginHost } from '../../../lib/api/plugin';
+import { TestIoHost } from '../../_helpers/test-io-host';
 
 let host: PluginHost;
 let credentialPlugins: CredentialPlugins;