Remove hole in the middle

There is additional cleanup that will come with the `DirPath` merge but at least the hole-in-the-middle is gone now.
This does not match the comment above, and i think this will result in data potentially being missed in a snapshot.

If the `featureStore.id` is different to `meta.featureStoreId` and the different factsets _only_ have partitions _before_ `meta.date`, then those partitions will not be read (i think).

Also, i think the above comment `OR the snapshot.date < date` should be `OR the snapshot.date <= date`