Extend pbs module get_header for inclusion proof validation

[eserilev]

in pbs/mod.rs overwrite BuilderApi's get_header fn to enable get_header_with_proof functionality

This should query the builder api's get_header_with_proof endpoint

The documentation here describes the get header with proof endpoint. This endpoint returns an inclusion proof that can be verified against the inclusion list that was generated by il-boost

Things to consider:

• How do we want to surface the inclusion list when performing proof validation? I introduced an inclusion list cache that might be useful here. The IL cache stores generated inclusion lists by slot #. When performing proof validation we can just fetch the IL from the cache
• Enable min bid functionality. This isnt super criticial at the moment, but eventually we'll want to consider min bid values. If a payload w/ inclusion list doesnt reach the min bid threshold, we'll probably want to revert to a payload that doesnt include our inclusion list (assuming its more profitable). Ideally we want to provide flexibility to users, they should be able to choose how altrusitic they want to be
• Would be nice to write some test cases eventually