Refactored the `CreateEnvelopeCommand` method in `Fake.cs` to delegate user authentication logic to the `WithAuth` method. Added a new `CreateEnvelopeCommands` method to generate multiple commands for a set of user IDs. Removed `ConstantsTests.cs`, which contained tests for the `Normalize` method of the `EnvelopeSigningType` enumeration, as the method or its tests are no longer relevant.