Add Prod transform, Add test_factory

lerobot/common/envs/transforms.py

@@ -0,0 +1,22 @@
+from typing import Sequence
+
+from tensordict.utils import NestedKey
+from torchrl.envs.transforms import ObservationTransform
+
+
+class Prod(ObservationTransform):
+
+    def __init__(self, in_keys: Sequence[NestedKey], prod: float):
+        super().__init__()
+        self.in_keys = in_keys
+        self.prod = prod
+
+    def _call(self, td):
+        for key in self.in_keys:
+            td[key] *= self.prod
+        return td
+
+    def transform_observation_spec(self, obs_spec):
+        for key in self.in_keys:
+            obs_spec[key].space.high *= self.prod
+        return obs_spec