StakeNet keeper doesn't handle delayed merkle root uploads properly

[buffalu]

Describe the bug
The StakeNet keeper doesn't handle delayed merkle root uploads properly.

If the merkle root upload takes awhile, the keeper doesn't handle that properly and will call copy_tip_distribution_account, which copies u32::MAX over for the MEV rewards. The keeper will then not go back and refresh it.

The keeper should handle this properly; it should account for slow merkle root uploads and ensure that the correct values are copied over

[abelmarnk]

Hey @buffalu, I’m planning to take this on since it’s been open for a while.

I think we can resolve it by adding a new field to the KeeperState struct, a HashMap from vote account keys to a Vec of epochs that have tip distribution accounts but no merkle roots yet.

The mev_earned fire handler would add to the map when it finds missing roots and retry them on subsequent fires. We could also enforce a max length or drop count per Vec to prevent unbounded growth.

I'll adjust the approach if you have any issues with this direction.