fix: (1) refactor in Agent.step() to fix out-of-order timestamps, (2) bug fixes with usage of preset/human vs filename values

[cpacker]

• refactor step() to fix out-of-order timestamps due to duplicate message
• correct use of persona and human - in many instances we were using them as persona/human_name, even though the values were expected to be the full value
• modify Preset model to contain a persona_name and human_name
  • was actually done in feat: added persona/human_name fields to Preset #1134
• pull these values in the REST API when returning information about the agents in the list_agents GET route

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Many of the line diffs are to fix a tangentially related bug where human_name and persona_name aren't being used correctly. For a future PR, we should strip this field and replace it with human_id and persona_id that point to the DB.

- [ ] TODO: strip human/persona_name, and refer to ID in table instead

[sarahwooders]

lgtm!