__setitem__: mistake in docstring and possible issue with Partition.BROADCAST and nccl comm

[mrava87SW]

In DistributedArray.__setitem__ the documentation should be fixed as it talks about UNSAFE_SCATTER instead of UNSAFE_BROADCAST (should mention that self.local_array gets updated for each individual rank without ensure it is communicated (like for BROADCAST) -

pylops-mpi/pylops_mpi/DistributedArray.py

Line 192 in 8b19ed3

`Partition.UNSAFE_SCATTER` - Local Arrays are assigned their

Also, some tests seem to suggest that when we have BROADCAST and use a multi-node multi-gpu setup, the DistributedArray.__setitem__ method seems to hung, likely at self._bcast - more investigation required.