fix: itest: fix wdpost proving epoch calculation

[rvagg]

Fixes: #12091 (I think)

Pulled out of #12105 where I was forced to figure it out and fix it.

[github-actions]

All checks have passed

[rvagg]

I changed this to wait one challenge window and re-collect deadline Info because I'm seeing odd behaviour locally with 47 and am wondering if there's a special case there

[rvagg]

I have a bit more confidence in this one after tinkering a bit more and grokking actors a bit better. One thing I'm doing now is not hitting the deadline open exactly, but waiting a bit, because I think we might be getting in too quick before cron updates the deadline index in state. It doesn't explain the 47/0 failures specifically but we'll see if that comes back after this. I'll pull it back in to #12105 and continue with this.

[ribasushi]

Fwiw I ran a number of itest runs since I included this and have not seen the issue crop up again

[rvagg]

ironically the test failed in CI for this branch, but it's different I think, might just be a timeout https://github.com/filecoin-project/lotus/actions/runs/9579047475/job/26410654516?pr=12113

[rvagg]

been re-running in CI and it seems solid; will continue to test in my niporep branch but I think this is good to go