Implement Verified Random Function (VRF) for Randomized Leader Election

As part of the security improvements for the Simplex Consensus Protocol implementation, we need to implement randomized leader election to resist censorship and adaptive adversary attacks.

**Requirements:**
- Integrate a VRF implementation (e.g., `schnorrkel` or similar Rust crate if applicable, or standard BLS/Ed25519 based VRF).
- Replace the current deterministic or round-robin leader election with a VRF-based selection.
- Ensure that the leader election is verifiable by other nodes.
- Update the consensus logic to validate the leader's VRF proof before accepting a block/proposal.

**Context:**
Simplex consensus relies on randomized leader election to mitigate risks where an adversary could target the known next leader. VRF provides a cryptographic way to select a leader randomly such that the choice cannot be predicted long in advance but can be verified by everyone once revealed.