* Remove deprecated ISavePolicyCommand interface and SavePolicyCommand implementation along with associated tests
* Refactor policy validation: remove IPolicyValidator interface and related implementations. Update PolicyServiceCollectionExtensions to eliminate deprecated methods. Adjust policy validator classes to remove IPolicyValidator dependency and streamline validation methods.
* Remove IPostSavePolicySideEffect interface and its implementation from the policy validation framework.
* Rename VNextSavePolicyCommand to SavePolicyCommand
* Continue renaming VNextSavePolicyCommand
* Refactor policy validation tests to use SavePolicyModel in ValidateAsync and side effect methods
* Refactor policy validators to directly use PolicyUpdate from SavePolicyModel in validation and side effect methods, improving code clarity and reducing method complexity.
* Rename test methods in PoliciesControllerTests and VerifyOrganizationDomainCommandTests to better reflect their functionality, enhancing clarity and consistency across the test suite.
* Refactor OrganizationUserNotificationPolicyValidator by removing unused methods and simplifying the implementation. Update corresponding tests to reflect these changes.
* Remove unnecessary nullable enable directives from policy validator files and update using statements for consistency.
* Rename policy validators to handlers
* dotnet format
