wrong local_world_size fallbacks to global world size with slurm

[JacoCheung]

Hi team, TorchRec has defined local_world_size and local_rank which gets initialized through several ENVs.

However, if the job is launched via slurm ( say, sbatch or srun), none of those is ENV defined.

I'm wondering if torchrec could add slurm env support rather than manually export LOCAL_WORLD_SIZE . Thanks!