some test cleanup, added driver runner tests, fix start_ts bug

[drmorr0]

• [x] I certify that this PR does not contain any code that has been generated with GitHub Copilot or any other AI-based code generation tool, in accordance with this project's policies.

Description

Add some tests for the driver runner, and fix the trace_store start_ts bug (TraceStore::start_ts would skip the first event in the simulation).

Testing done

• make itest (added new test)
• TODO: manual testing

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 74.92%. Comparing base (e5f05c5) to head (87bc0c1).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #101 +/- ## ========================================== + Coverage 69.67% 74.92% +5.24% ========================================== Files 38 38 Lines 1916 1922 +6 ========================================== + Hits 1335 1440 +105 + Misses 581 482 -99 ```

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