fix: seed timer at training start to avoid AttributeError

gcsfs/tests/perf/macrobenchmarks/workloads/hf-pytorch-lightning-cpu/helm_chart/llama_3_1_8b_cpu_sim.py

@@ -284,6 +284,12 @@ def __init__(self):
         super().__init__()
         self.ckpt_time = 0.0
 
+    def on_train_start(self, trainer, pl_module):
+        # Initialize timer at training start to avoid AttributeError when resuming mid-epoch
+        # (where on_train_epoch_start is skipped).
+        self.start_time = time.perf_counter()
+        self.ckpt_time = 0.0
+
     def on_train_epoch_start(self, trainer, pl_module):
         # Start timer at the beginning of the epoch to capture the first batch's data loading time
         self.start_time = time.perf_counter()