[bug] get_item_from_future() is not supported for ClusterExecutors

Example: 
```python
from executorlib import get_item_from_future
from executorlib.api import TestClusterExecutor

def return_dict(i):
    return {"i": i}

with TestClusterExecutor() as exe:
    f1 = exe.submit(return_dict, i=1)
    f2 = exe.submit(return_dict, i=get_item_from_future(f1, key="i"))
    print(f2.result())
```

The same example works fine with the `SingleNodeExecutor`. 