Investigate whether memory usage can be reduced by not caching Promise objects

My strategy would be to wrap cached promises with a new `CachedPromise` class.

```ts
class CachedPromise {
constructor(promise) {
this.promise = promise
promise.then((result) => {
this.result = result
this.promise = null
}, (error) => {
this.error = error
this.promise = null
})
}
then() {}
catch() {}
finally() {}
}
```