Fix missing information on pending task results

[bjester]

Summary

Description of the change(s) you made

• Manually sets the task name and kwargs on the task result object
• Adds a new test that validates task result models contain necessary information
• Updates existing fetch_or_enqueue test to ensure it matches results created through enqueue

Manual verification steps performed

Ran the tests

References

Resolves #3820

Comments

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[bjester]

I think the test failures and flip-flopping might be caused by the missing add_pending_result-- I'm going to revert and just set the fields where we're setting user and channel

[rtibbles]

Code changes make sense, and tests give the assurance.