feat(base_layer): checkpoint quorum validation

[mrnaveira]

Description

Refactored the base layer committee validation for checkpoints:

• Now it's based on HashSet of VNC public keys: one for the constitution and other for the checkpoint
  • Surprisingly, clippy warns about mutable_key_type for using PublicKey types as the keys in the HashSet. I'm not sure where the mutability comes from. I decided to ignore that rule for the validation function
• The existing validation of members is now done by checking the difference of the public key sets
• The new quorum validation is done by checking the intersection of the public key sets

Motivation and Context

The base layer need to validate if the quorum of an incoming checkpoint is met. The minimum quorum for checkpoints is specified in the ContractConstitution, in the checkpoint_params.minimum_quorum_required field

How Has This Been Tested?

New unit test to check both successful and failing scenarios regarding quorum conditions

[sdbondi]

I like the use of HashSet for ease of code understanding, but it does result in some extra clones + heap allocations which could be avoided with a for loop. I think a HashSet<&PublicKey> would also work and use less memory (allocates only n words/usize).

In any case, happy for it to go in 👍