Feature: metadata/status

We use cachified in many different contexts in our apps, and we love it.
And we would really love to have the possibility to see cache status from a cache result, in some way or another.

``` typescript
const cachifiedResult = await cachifiedWithMetadata({
key: `user-${userId}`,
cache: ourCache,
async getFreshValue() {
...
},
ttl: 300_000,
});

console.log(cachifiedResult.status) // "HIT", "MISS" or "REVALIDATING"
console.log(cachifiedResult.value) // Cached, or fresh value
```