Update EveryNSteps preservation policy.

PiperOrigin-RevId: 805206191

Author: abhishek002002

checkpoint/orbax/checkpoint/_src/checkpoint_managers/preservation_policy.py

@@ -157,7 +157,17 @@ def should_preserve(
   ) -> Sequence[bool]:
     if self.interval_steps == 0:
       raise ValueError("interval_steps must not be 0.")
-    result = [ckpt.step % self.interval_steps == 0 for ckpt in checkpoints]
+    result = []
+    previous_step = None
+    for i, ckpt in enumerate(checkpoints):
+      if i == 0:
+        result.append(True)  # Always preserve the first checkpoint.
+        previous_step = ckpt.step
+      elif ckpt.step - previous_step >= self.interval_steps:
+        result.append(True)
+        previous_step = ckpt.step
+      else:
+        result.append(False)
     _log_preservation_decision(
         f"EveryNSteps (interval_steps={self.interval_steps})",
         checkpoints,