[Feature]: New and replacement integration / regression tests

Description

Two of the three existing integtests in the trigger repo are broken. This has been true for a while, and I am going to remove them, for now.

However, the functionality that they once tested would still be good to have. So, I'm filing this Issue to remind us to come back to these tests someday.

• the tc_time_outside_window_test.py test attempts to validate the expected behavior of TriggerCandidate fragments when the TriggerDecision request window doesn't include the TC time. Unfortunately, at the moment, it is not clear to me how we expect TC fragments to be populated in various conditions, and I'm not sure of the current way (or ways) that we specify TC times versus other times.
• the td_leakage_between_runs_test.py test attempted to validate the graceful stopping of TriggerDecision messages between the MLT and the DFO. There are comments in this this PR. The stumbling block to getting this integtest working again now is that it is not clear how we would configure the conditions that are likely to demonstrate the problem

In summary, it would be good to bring back these tests someday.

Independent of that, we can imagine other tests that would be useful. Such as ones that validate the behavior of TC merging.

Potential impact radius

Small/Isolated

Reason for change

Validating expected functionality is a good thing

Suggested implementations

No response

Testing suggestions

No response

Anything else?

No response

Start by reviewing the removed or broken tc_time_outside_window_test.py and td_leakage_between_runs_test.py integration tests, then read the comments in PR 249. Clarify how TriggerCandidate fragments and TriggerDecision request windows are configured before restoring tests; done means the replacement regression tests run successfully, with any useful TC-merging coverage included.