eip7251: Do not change creds type on consolidation

[mkalinin]

This PR introduces the following changes to the consolidation request processing:

1. Disallows consolidations if the target doesn’t have 0x02 creds
2. Does not switch to compounding when consolidation happens

Which effectively changes consolidation flow in a way that stakers will have to do it in two steps:

1. Switch the target to compounding creds via switch to compounding request (consolidation with source==target)
2. Consolidate the source balance to the target

This change disallows an unauthorized update of withdrawal credential type and simplifies the protocol by trading off consolidation UX. To alleviate the UX downgrade this PR increases the MAX consolidation requests per block to 2 which allows to accommodate creds switch and consolidation in a single block.

Supplants #4006

ToDo

• Change MAX parameter in the Consolidation Smart Contract
• Update tests

[fradamt]

Lgtm.

Imo the UX impact is quite limited and it makes sense to get rid of this strange behavior, even if it's not really an attack vector.

[ralexstokes]

I like that this simplifies the complexity of the state transition and general validator lifecycle state graph

it also handles the unauthorized consolidation issue

will need to fix tests but I think we should 🚢 it

[lucassaldanha]

I agree that this is not a great UX but simplify the complexity of state transition. It also prevents anyone from causing a permanent side-effect on someone else's validator (0x01 -> 0x02 unwanted creds change).

[fradamt]

Something else to mention about the impact is that the primary use case is staking pools consolidating, in which case needing to call the contract 63 times versus 64 times doesn't really make any difference

[rolfyone]

LGTM