DAL: add shard_proof and verify_shard to the protocol environment
What
Add shard_proof and verify_shard to the protocol environment.
On top of !15659 (merged).
Why
The protocol will need those:
- a shard with its proof will be included in the new DAL accusation operation
- the protocol needs to be able to check that the included shard is valid
Edited by Eugen Zalinescu