Extract Header-only methods of Consensus to a separate trait

[klkvr]

Describe the feature

With #12451 Consensus is now generic over header and body

reth/crates/consensus/consensus/src/lib.rs

Line 47 in e686fcc

pub trait Consensus<H = Header, B = BlockBody>: Debug + Send + Sync {

However, in components which only know the header type we can't provide Consensus with Body generic, e.g

reth/crates/net/downloaders/src/headers/reverse_headers.rs

Line 70 in e686fcc

consensus: Arc<dyn Consensus<H::Header>>,

To address this, we'll need a separate trait which is alike Consensus but only operates on headers.

Steps:

1. Inroduce trait trait HeaderValidator<H = Header> and move Consensus methods which only need header to it. Those include validate_header, validate_header_against_parent, validate_header_range, validate_header_with_total_difficulty
2. Inroduce bound Consensus<H = Header, B = Body>: HeaderValidator<H>
3. Fix trait impls and import HeaderValidator where needed

Additional context

No response

[0xriazaka]

Can i work on this?