Declarative hook configuration object.

Pass this to the TransformationHookManager constructor to register one or more hooks in a single expression:

const manager = new TransformationHookManager({
  beforeTransform: [(ctx) => console.log('start', ctx.name)],
  afterTransform:  [(ctx) => console.log('done', ctx.durationMs + 'ms')],
  onError:         [(ctx) => console.error(ctx.error)],
});

All three arrays are optional. An empty config object is equivalent to no hooks at all.