feat: pectra compatibility

[ypatil12]

Updates checkpoint proof system to be Pectra compatible. The breaking change to EigenPods is the BeaconState container increasing to have 37 fields, which results in the tree height to be > 5.

Overview

• We hard code the proof timestamp in the BeaconChainProofs library, since the mainnet proof timestamp will be telegraphed 2-3 weeks in advance of the upgrade. I'm particularly looking for feedback on this approach

• To mitigate all possible risks, the other option would be to have the OpsMultisig set the proofTimestamp closer to fork time (this could not be the owner because on mainnet this is the ExecutorMultisig)

EigenPod

• Updated balance container and validator container proofs to pass in a proof timestamp to check against which tree height to use for the beacon state
• Note that since the 4788 oracle returns the PARENT beacon block root, our check against the pectra fork timestamp returns the previous tree length for proofs that are <= pectraForkTimestamp

Deprecation Plan

• Post pectra, we can upgrade the EigenPod to deprecate the fork timestamp case handling once all in progress pre-Pectra checkpoints have been completed

TODOs

• Unit Tests
• Integration Tests simulating upgrade
• Mekong Deployment

[eigenmikem]

AFAIK the fork timestamp has never been altered once broadcast, at least not in the last few years, so I think hardcoding it is fine

[wadealexc]

Hmm, I wonder about the usage of getParentBlockRoot above.

Can beaconTimestamp belong to the block after the fork, but the proof itself is over the parent block (aka pre-fork)?

[wadealexc]

Is this PR targeting testnet?

We're going to need a different PR for mainnet, since that's landing before slashing, right? (This EigenPod file is compatible with testnet slashing, but not mainnet)

[ypatil12]

Is this PR targeting testnet?

Yup, targeting testnet. There will be a separate mainnet PR. cc @wadealexc