Some BlockOps need more logic at the Volume layer

Some BlockOp enums might need to be updated to provide additional context.

Specifically:

    QueryExtentSize {                                                           
        done: BlockRes<Block>,                                                  
    },                                                                          
    QueryWorkQueue {                                                            
        done: BlockRes<WQCounts>,                                               
    },                                                                          
    ShowWork {                                                                  
        done: BlockRes<WQCounts>,                                               
    }
```

These block ops make sense when a single upstairs exists behind the object that supports the trait.
For example, `Guest` only ever has three downstairs and one work queue.

However, with a `Volume`, you could have multiple sub-volumes and a read only parent.  So what is returned in this case can no longer be represented by a single object, or if it is, it has lost some information that the caller might want.
In the case of `QueryExtentSize`, a single value here for a `Volume` is only correct if everyone happens to share the same extent size, or if there is only a single sub volume.

Start by locating the BlockOp definitions and the Volume and Guest implementations that handle QueryExtentSize, QueryWorkQueue, and ShowWork. Compare the information available for single and multiple sub-volumes, then document a representation that preserves the needed context and update the relevant tests to verify it.