Describe the bug
comms_iface has no virtual destructor
(https://github.com/rapidsai/raft/blob/branch-22.02/cpp/include/raft/comms/comms.hpp#L91).
This means std_comms or mpi_comms destructor will not be called when comms_t's destructor is called and std::unique_ptr<comms_iface> impl_; gets destructed (https://github.com/rapidsai/raft/blob/branch-22.02/cpp/include/raft/comms/comms.hpp#L608).

Also,

initialize_mpi_comms with the given MPI_Comm comm calls mpi_comms with owns_mpi_comm = true
(https://github.com/rapidsai/raft/blob/branch-22.02/cpp/include/raft/comms/mpi_comms.hpp#L442).
cuGraph calls initialize_mpi_comms(&handle, MPI_COMM_WORLD) and as owns_mpi_comms is set to true, mpi_comms destructor will call MPI_Comm_free. This is erroneous.

Additional context
virtual ~comms_iface() {} should be added to class comms_iface.
initialize_mpi_comms should call mpi_comms with owns_mpi_comms = false (and caller should be responsible for destroying comm).