Const array enum support

[maraisr]

Thanks again so much for this library, it's literally a dream.

I ran up against something recently, in wanting to have runtime enum values as well. I did not really want to use TypeScripts enum mechanism (not a fan). Though maybe that is the canonical way to do that, in which case happy to close this pr.

But yeah, I wanted to do something like this:

const ALL_SHOW_STATUSES = ["DRAFT", "SCHEDULED", "PUBLISHED"] as const;

/** @gqlEnum */
type ShowStatus = (typeof ALL_SHOW_STATUSES)[number];

/** @gqlInput */
type ShowStatusFilter = { anyOf: ShowStatus[] };

function applyFilter(filter: ShowStatusFilter) {
  // Because ALL_SHOW_STATUSES is a real array, we can compare at runtime
  if (filter.anyOf.length === ALL_SHOW_STATUSES.length) {
    // No filtering needed — every status was selected
    return getAllShows();
  }
  return getShowsByStatus(filter.anyOf);
}

You know, have the ability to see if the user-provided set includes all enum variants. I did not like the fact that I needed to define those twice:

/** @gqlEnum */
type ShowStatus = "DRAFT" | "SCHEDULED" | "PUBLISHED";
const ALL_SHOW_STATUSES: readonly ShowStatus[] = ["DRAFT", "SCHEDULED", "PUBLISHED"];

Like yeah, I do still have type-safety so if I add an item to one, that it exists in the other. But my OG DRY self wanted only one place to define that.

So here we are, a PR that adds that support. What do you think @captbaritone? Is this a direction/feature/inevitably code you'd likely need to maintain, something you're interested in?

I'll be honest, I've never worked in this codebase before. And definitely didn't quite have the brain space to fully understand it (though would like to help moving forward). So asked Amp to to help me: https://ampcode.com/threads/T-019cc14e-74ed-75ef-8fbe-339f5d582962

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[captbaritone]

Thanks for the PR! I took ideas from here and from #205 and implemented a somewhat different approach in #225.

You can install grats@main to try it out.