Request: exposing token utilization, getValue

This is a following conversation in the beta components thread.

Context: Currently the api only provides you the next time that you can retry at. We reverse engineered the convex helper rate limiter to show a user their personal bucket status for that user account. Within this usecase sharding is not necessary avoiding the need to query a sample set. But I could see the use of that with a bigger token bucket with more resolution and activity.

Ian suggested:
```
const value = await rateLimiter.getValue(ctx, "myLimit");
// to just sample a few shards for efficiency / avoiding OCCs
const value = await rateLimiter.getValue(ctx, "myLimit", { sampleShards: 3 });
```
This works for us. But may have limited use for other users who don't want to reverse engineer it.

I think it would be nice to have it optionally available when you call rateLimiter.check