Added basic block production to Caplin.

[Giulio2002]

This PR also does the following additional things:

• Introduces correct JSON marshalling/unmarshalling to all objects
• BaseFeePerGas marshalled as integer on json caplin-wise
• Reduced dumpSlotsStates from 32 to 4 for better performance during reorgs
• Added full lock for OnAttestation

Block Production

This section highlights how GET eth/v3/validator/blocks/{slot} creates a block and then publishes it.

The validator client will do execute 2 steps when producing a beacon block.

1. Production step: tell the beacon client to create a block and return it.
2. Publishing step: Sign the block with the proposer private key, and send it back for publishing to other nodes.

Block creation

Let's first look at how block creation happens.

So Caplin needs to do 2 things to successfully create a block:

1. Asking the Execution Layer for the Execution block
2. Retrieve Consensus Operations to include in the block (Attestations/VoluntaryExits, etc...)

Execution block

For the execution block, it is quite simple, we ask Erigon to produce us a block through the AssembleBlock function avaiable on the Erigon Eth1 API. We treat erigon as a black box so we do not need to worry too much about this. However, we also need to handle Blob bundles, so that later, when we need to publish a block. we can publish the bundles alongside the block (it is important that peers both receive block and the blob or we will fail a check). (Erigon will also gives us the bundle). Right now, we store the blob bundle in an LRU which has size set to 8 blocks worth of blobs. Note: we use an LRU for the convenient eviction policy.

Operations

TODO.

Operations inclusion has not been implemented yet, the execution block is the only thing being delivered.

Block publishing

After we produce the beacon block, we will send it back to the Validator Client, which will sign it and re-forward it to the rest of the network.

The flow is straightforward, when we receive the block we simply:

1. pack the block with the blobs the Execution Layer gave caplin during block production
2. Start a separate thread where we import the block into Caplin's database and forkchoice alongside the blobs..
3. Publish blobs and blocks to the P2P.

[Giulio2002]

Proof-of-Work