Add a separate execution-layer validation section with the block validity rule changes.

Detailed list of changes:

• use data gas for all accounting (instead of number of blobs)
  • update calc_excess_data_gas()
  • update block validation accounting
• add block validation section
  • move data gas logic to this section
  • modify sufficient balance check
  • add per-block data gas limit
  • require at least one blob per blob tx
  • check prefix byte

There is still an open question as to how to handle the relationship between data gas limit and CL max blobs per block limit, however this is considered out of scope for this PR.