add ssd ods stats

Summary:
add ods stats

1. rocksdb mem stats
2. rocskdb  internal metrics enablement
3. rocksdb io performance stats
4. ssd offloading stats reporting
5. prefetch duration calculation

Differential Revision: D59740171

torchrec/distributed/tests/test_model_parallel_nccl_ssd_single_gpu.py

@@ -70,6 +70,7 @@ def _load_split_embedding_weights(
             weight,
             torch.as_tensor([height]),
             table_id,
+            False,  # is_bwd
         )
         cum_sum += height