Harden integration-test setup and verification helpers #1758

Summary

Improve the robustness of the SecurityService.IntegrationTesting.Helpers and related integration-test steps so setup failures and incomplete assertions are detected instead of allowing scenarios to continue with invalid state.

Included changes

• Enforce requested step counts in collection/table-based integration steps.
• Verify created API scopes, API resources, clients, identity resources, roles, and users by reading them back from the service.
• Compare persisted fields and nested collections, including exact collection counts and duplicate detection where applicable.
• Validate all configured users in the MFA scenario.
• Validate existing OpenID Connect identity resources instead of silently accepting same-name resources with different configuration.
• Propagate supplied cancellation tokens through read operations.
• Harden integration certificate cleanup for partial creation and disposal failures so cleanup does not mask the original failure.

Verification

• dotnet build SecurityService.IntegrationTests\SecurityService.IntegrationTests.csproj --no-restore -v minimal
• dotnet build SecurityService.OpenIdConnect.IntegrationTests\SecurityService.OpenIdConnect.IntegrationTests.csproj --no-restore -v minimal
• git diff --check

Both builds succeeded. Runtime Docker-backed integration tests were not run as part of this change.

Follow-up

• Resolve existing package vulnerability warnings and nullable warnings separately.