Check if req is included in another req

[franzaps]

Performance optimization if ever needed:

Relative to merging, a req can be included in another one, for example:

{authors: [a], kinds: [1]} is included in {authors: [a,b], kinds: [1,2]}

So instead of doing storage.requestCache[r.subscriptionId]![r] and cache-miss, it could find the necessary models as a subset of a model list associated to a "greater" req.

Probably wouldn't work for relays if they have a hard limit around 500-1000 events. But it would work for the request cache.