dynamically add new loader functions to Cache

Hey, I think that being able to colocate data fetching and resolvers is a good pattern some times, so I tend to wrap the API with a conditional check (to dynamically register the loader), is this library open for a PR adding that functionality?

const loaderFactory = new Factory()

function addLoader<T, O>(name: string, fn: Batchfn<T, O>) {
  loaderFactory.add(name, fn)
  return async (loader: Cache, key: T): Promise<O> => {
    if (!loader[name]) {
      loader.prototype[name] = loaderFactory.Cache.prototype[name]
    }
    return await loader[name](key)
  }
}

getFoo = addLoader(...)
getFoo(loader, id)

Start by reading the existing Cache and Factory APIs and how loader functions are currently registered. Determine the intended behavior for conditional registration and the addLoader flow shown in the issue, then confirm that dynamically added loaders work without changing existing loaders.