Modify block interface to support DA

[jbearer]

• Type for full block with data
• Type for block commitment
• Interface to add transactions to the full block
• Interface to get a commitment from full block
• Change all replica logic to work with the commitment, not the full block

[nmccarty]

• Type for full block with data
  Using the old Block
• Type for block commitment
  Using a new type wrapper BlockCommitment
• Interface to add transactions to the full block
  Already exists on old block type
• Interface to get a commitment from full block
  Added block_commit method to Block
• Change all replica logic to work with the commitment, not the full block

[nmccarty]

We now have a set of wrapper types in da.rs that wrap an existing block type into a family of types that only work on the commitments to those blocks