The Record class was already capturing a unix timestamp, but it was incorrectly
converting it to ISO format when sending back to the client.
Updating the model to return the correct timestamp necessitated a minor change
to one of the tests because `botocore` converts non-timezone aware timestamps
to local time.
* Support for CloudFormation stack resource deletion via backend resource method
delete_from_cloudformation_json() via parse_and_delete_resource().
* Correction to the inappropriate inclusion of EndingSequenceNumber in open shards.
This attribute should only appear in closed shards. This regretfully prevents
confirmation of consistent record counts after split/merge in unit tests.
* Added parameters/decorator to CloudFormationModel method declarations to calm-down Pycharm.
Co-authored-by: Joseph Weitekamp <jweite@amazon.com>
