Refine events detection behaviour + backend

[piotmag769]

Which components does the task require to be changed? (think hard pls)

snforge

Description

Currently we check if the event should be caught by any spy, if it should, we add it to detected events.
Then in fetch_events we consume the events that the spy should catch, deleting it from detected events vector.

This results in a weird coupling of logic and causes unintuitive behaviour when spying on the same contract with multiple spies.

We should instead keep a queue for each spy and push/pop events from it accordingly

[Arcticae]

Irrelevant because of #1889