feat(pairwise): allow passing evaluator directly to wait for evaluation to complete

[dqbd]

Allows the following syntax

const pairwise = await evaluateComparative(
  [
    evaluate((input) => ({ foo: `first:${input.input}` }), {
      data: TESTING_DATASET_NAME,
    }),
    evaluate((input) => ({ foo: `second:${input.input}` }), {
      data: TESTING_DATASET_NAME,
    }),
  ],
  {
    evaluators: [
      (runs) => ({
        key: "latter_precedence",
        scores: Object.fromEntries(runs.map((run, i) => [run.id, i % 2])),
      }),
    ],
  }
);