Feature: Allow scorer functions to return arrays of scores

Feature Request: Allow scorer functions to return arrays of scores

Problem

Currently, scorer functions can only return a single Score object. However, some use cases involve LLM graders that assess multiple criteria in a single call and return multiple pass/fail results.

Use Case

I have an LLM grader that performs a one-shot assessment of multiple criteria and returns a pass/fail for each criterion. For example, evaluating if a response is accurate, complete, and clear - all in a single LLM call for efficiency.

Currently, I need to either:

• Make separate LLM calls for each criterion (inefficient and costly)
• Write custom logic to split the results into multiple scorer calls
• Use only a single aggregate score

Proposed Solution

Allow scorers to return either a single Score or an array of Score[], which would be flattened into the final scores array.

This appears to be achievable with a simple .flat() here: https://github.com/mattpocock/evalite/blob/e04b48ff260d8966e1fa3b2a6955c9abae9adcb9/packages/evalite/src/evalite.ts#L89 (plus type changes to allow Score | Score[]).

Start in packages/evalite/src/evalite.ts at the linked location around line 89, then trace the scorer result types. Update the accepted result shape and flatten returned score arrays into the final scores array; done means both single Score results and arrays of Score results are supported.