[TASK] Implement resiliency logic in the event of failure at any step.

[drewstone]

Overview

At any step in the improvements listed in #529, something can go wrong. We must identify this and provide a path for recovering from these issues resiliently. For example, if we parallelize signing operations and a certain set fails to sign their allocated proposal, we must re-allocate that proposal.

Tasks

• Identify the parts in which the Signing manager improvements will fail.
• Provide implementation improvements that reduce the failure rate and adapt to failures.
• Test with test harness.