feat: add LeRobot v3 metadata validation checks

lerobot_validator/__init__.py

@@ -9,6 +9,14 @@
 
 from lerobot_validator.validator import LerobotDatasetValidator
 from lerobot_validator.gcp_path import compute_gcp_path
+from lerobot_validator.v3_metadata_checker import LerobotV3MetadataChecker
+from lerobot_validator.v3_checks import Issue, validate_v3_dataset
 
-__all__ = ["LerobotDatasetValidator", "compute_gcp_path"]
+__all__ = [
+    "LerobotDatasetValidator",
+    "compute_gcp_path",
+    "LerobotV3MetadataChecker",
+    "Issue",
+    "validate_v3_dataset",
+]
 

lerobot_validator/metadata_validator.py

@@ -139,8 +139,14 @@ def _check_start_timestamp_format(self) -> None:
         for idx, row in self.df.iterrows():
             timestamp = row.get("start_timestamp")
 
-            # Skip if missing (will be caught by required columns check)
+            # Null timestamps are not allowed — every episode must have a
+            # valid collection start time.
             if pd.isna(timestamp):
+                episode_id = row.get("episode_id", f"row_{idx}")
+                invalid_timestamps.append(
+                    (idx, episode_id, timestamp,
+                     "start_timestamp is missing/null (every episode requires a valid timestamp)")
+                )
                 continue
 
             # Try to convert to float (epoch time should be numeric)