Introducing Evals

Introduces Evals for Hex Agents, a testing framework that uses an LLM-as-judge to evaluate agent performance on data analysis tasks. Evals allow for grading the agent's reasoning and behavior, not just the final answer, by assessing tool usage, clarification requests, and appropriate refusal to answer. Test cases are defined in version-controlled files and executed via the Hex CLI. The feature supports Context Previews for testing changes before publishing and running configuration sweeps across different LLMs. It aims to make agent quality and cost measurable and improvable, turning agent management into a quantifiable process.