Create ssz type: SubmitBlockRequestV2Optimistic

[michaelneuder]

📝 Summary

Creating the type and SSZ encoding needed for the v2 optimistic builder submissions.

This type implements the standard SSZ interface

MarshalSSZ
UnmarshalSSZ
MarshalSSZTo
SizeSSZ

We also define a custom decode that only parses the header part of the bid UnmarshalSSZHeaderOnly.

This follows up on the series: #479, #491, #494, #498, #513, #514, which aim at reducing the diff and productionizing #466.

⛱ Motivation and Context

SubmitBlockRequestV2Optimistic is the v2 request from the builder to submit a block. The message must be SSZ encoded. The first three fields are at most 944 bytes, which fit into a single 1500 MTU ethernet packet. The UnmarshalSSZHeaderOnly function just parses the first three fields, which is sufficient data to set the bid of the builder. The Transactions and Withdrawals fields are required to construct the full SignedBeaconBlock and are parsed asynchronously.

Header only layout:
[000-236) = Message   (236 bytes)
[236-240) = offset1   (  4 bytes)
[240-336) = Signature ( 96 bytes)
[336-340) = offset2   (  4 bytes)
[340-344) = offset3   (  4 bytes)
[344-944) = EPH       (600 bytes)

📚 References

https://notes.ethereum.org/@mikeneuder/optimistic-v2

https://github.com/michaelneuder/optimistic-relay-documentation/blob/main/towards-epbs.md#optimistic-relay-v2-header-only-parsing

---

✅ I have run these commands

• make lint
• make test-race
• go mod tidy
• I have seen and agree to CONTRIBUTING.md

[codecov-commenter]

Codecov Report

Merging #518 (a1b3ad0) into main (36d55f7) will increase coverage by 1.08%.
Report is 1 commits behind head on main.
The diff coverage is 55.08%.

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@@            Coverage Diff             @@
##             main     #518      +/-   ##
==========================================
+ Coverage   32.15%   33.24%   +1.08%     
==========================================
  Files          24       24              
  Lines        4876     5078     +202     
==========================================
+ Hits         1568     1688     +120     
- Misses       3116     3171      +55     
- Partials      192      219      +27     

Flag	Coverage Δ
unittests	33.24% <55.08%> (+1.08%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files Changed	Coverage Δ
common/types.go	15.01% <55.08%> (+12.92%)	⬆️

... and 1 file with indirect coverage changes

[metachris]

what's the upgrade path for deneb?

[michaelneuder]

the deneb blocks will have the kzg commitments. The ExecutionPayload and the ExecutionPayloadHeader each have two new fields, blob_gas_used and excess_blob_gas for sure will need to include these types because they are part of what the validator signs over.

[avalonche]

are you making a versioned struct for future upgrades?