fix(spool): Treat (key1, key2) and (key2, key1) as distinct stack keys

[jjbayer]

#3863 features an optimization that treats project key pairs (key1, key2) and (key2, key1) as the same stack key. This keeps the number of entries in the priority queue minimal.

However, this prevents backward compatibility, because self-hosted users might still have existing DBs with two separate entries for the same key pair, and querying for both combinations is unnecessarily slow.

#skip-changelog

[iambriccardo]

LGTM, we might want to add a metric to measure how many times a combinations of the same projects is stored twice in the map.