[Altair] Update op pool tests to advance state correctly

[realbigsean]

Issue Addressed

N/A

Proposed Changes

After making some updates related to @michaelsproul 's comment here, I realized the op pool tests are just setting the slot clock rather than advancing the state before running scenarios, so they're running on top of the genesis state as opposed to a state with finalized and justified epochs. This was introduced in #2315, where I added the beacon harness into these tests

Additional Info

This makes the tests take much longer to run...

[michaelsproul]

Hmm, they do take quite a bit longer with this change.

Do the tests fail with your new changes when you take out the state advance?

One option to make them run faster would be to use the minimal spec rather than mainnet, although when I tried that just now everything broke and I didn't have the patience to go into debugging it

[realbigsean]

Do the tests fail with your new changes when you take out the state advance?

I just need a state advance of one slot for the sync contribution tests. And it seems like the attestation tests don't actually need the advanced state.. all the scenarios use attestations for the current slot. I think I was a little misled by the very specific slot_offset used.

So I can close this PR, and in my sync pool PR I'll advance the state as I need it. If we want to add scenarios where we put attestations from the previous epoch into the op pool, we may need something like this though.