Add Checkpointing / Resume Functionality for Experiments

[AWbosman]

Background

Currently, if an experiment run is interrupted (e.g., due to manual cancellation, a node going down, or other unexpected issues), it is not possible to resume the experiment without restarting everything from scratch.
This wastes time and compute, especially for large-scale experiments.

Proposal

Implement a checkpointing / resume system that allows VERONA to continue experiments from where they left off.

Key ideas:

• Track which experiment instances have already been completed (e.g., store this in a results CSV or a lightweight database).
• On restarting, check which instances are missing or incomplete.
• Continue execution only for the incomplete instances.

Benefits

• Saves time by avoiding re-running completed instances.
• Makes VERONA more robust to interruptions and cluster instability.
• Improves user experience for long-running experiments.