future: value(fs) is better than lapply(fs, value)

Hello, these days, as the author of Futureverse, I recommend to use:

```r
ys <- value(fs)
```
instead of:

```r
ys <- lapply(fs, value)
```

One reason is that it `value(fs)` on a set of futures `fs` supports early stopping in case of errors and interrupts. For instance, if the user interrupts the processing, `value(fs)` will cancel all active futures, which results in `value(fs)` exiting much sooner. Same happens if one of the futures result in an error -- all other futures will be canceled and then the error is produced. This will not happen when using `lapply(fs, value)`.

Here's one example where you could update your code accordingly:

https://github.com/greta-dev/greta/blob/ddc98fb47c5f278465035abeb1b32633febb3737/R/inference.R#L388