feat: add openadapt-types dependency and _AgentOutput schema

[abrichr]

Summary

• Add openadapt-types>=0.1.0 to core dependencies — the canonical Pydantic v2 action schema for the OpenAdapt ecosystem (converges BenchmarkAction, openadapt-ml Action, omnimcp ActionDecision)
• Add _AgentOutput Pydantic model for future Outlines JSON schema constrained decoding (outlines.json(model, _AgentOutput))
• Does NOT change the system prompt — DSL format remains default per fix: critical TRL trainer bugs — wrong prompt, ignored task_ids, DSL parsing #236 fix

Cherry-picked from closed #237, which incorrectly replaced the DSL system prompt with JSON (re-introducing the garbage output bug fixed in #236).

When to use _AgentOutput

Once a model is SFT'd on JSON action format, switch constrained decoding from regex to JSON schema:

# Current (DSL regex, default):
constraint = outlines.regex(ACTION_REGEX)

# Future (JSON schema, after SFT on JSON):
constraint = outlines.json(_AgentOutput)

Test plan

• 27 TRL tests pass
• 1449 passed, 54 skipped in full suite
• System prompt unchanged (DSL format)

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