consensus: make Header nonce u64

[tcoratger]

Component

consensus, eips, genesis

Describe the feature you would like

At the moment, the nonce field in Header consensus struct is B64:

alloy/crates/consensus/src/header.rs

Line 77 in e01492a

pub nonce: B64,

To match the definition we expect in reth and other repos:

https://github.com/paradigmxyz/reth/blob/3a255a1cabd1f19399b42c1fe9bdcc130ac61c2e/crates/storage/codecs/src/alloy/header.rs#L30

it would be nice to make it u64, would you agree @mattsse ?

Additional context

No response

[Rjected]

Just noting that to do this correctly, we also need to bring back the Encodable / Decodable implementations from before reth switched to alloy types, otherwise this would break RLP encoding.

[mattsse]

technically this is 8bytes, I think we can keep B64, dont think this type is used that often and we can add a helper that converts this to u64