Function reset 

pub fn reset(registry_path: &Path) -> Result<ResetResult>

Reset all node state: remove all data directories, log directories, and clear the registry.

This function:

1. Loads the registry (with file lock)
2. Iterates over all registered nodes
3. Removes each node’s data directory
4. Removes each node’s log directory (if set)
5. Clears the registry (empties nodes, resets next_id to 1)

Does NOT check if nodes are running — callers must verify that first.