[DRB] - Start the DRB calculation two epochs in advance

[shenkeyao]

Closes #3857.

This PR:

• Calls the DRB function in the vote task to start the computation for two views in advance.
• Updates the vote task type to include spawned DRB computation tasks.
• Moves and updates the DRB implementation file.

This PR does not:

• Handles the use of the DRB result, which will be done in the upcoming PRs.

Key places to review:

• All files, but the main changes are in handlers.rs.