Add support for `discover` method to `StateLifecycleManagerImpl`

We may need the following method to discover snapshots in a given directory
```
/**
* Returns a list of paths to snapshots discovered in the specified directory.
*
* @param sourcePath the path to the directory
* @return a list of paths to snapshots
*/
public static List discover(Path sourcePath) {
// implementation
}
```

Start by locating StateLifecycleManagerImpl and reading its existing snapshot lifecycle methods. Determine which files define snapshot storage and whether tests cover discovery; the issue does not specify the snapshot naming or filtering rules, so clarify those expectations before implementing and testing discover(Path).

Written by the indexing model from the issue text.