Have multiple workers to speed up fetching slots

[viper7882]

Have multiple workers to speed up fetching slots

[ggrieco-tob]

Have fetch slot to leverage multiple workers to parallelly retrieve the slots

We have not implemented this because it will quickly hit the fetching limits for most of public RPCs

Cache the slots once they are retrieved

This is already implemented, but you don't see it very easily because what I explained in #1261.

[viper7882]

Thanks @ggrieco-tob. Understand concern over RPC fetching limit and we are good for the cache implementation. Let me close the issue

[ggrieco-tob]

No problem, please keep reporting RPC related issue if you have them, we want to make sure this can be used for real-world testing. I'm also considering writing a small tutorial in building-secure-contracts to help users.