feat(envs): add envs pre-post processor (#2474)

* more changes

* working changes

* more changes

* more fixes

* fix style

* more

* clean

* put axis-1

* more fixes

* more styling fixes:

* iterate on review:

* more changes

* add env processor

* style

* more changes

* add docs

* fix imports

* fix test, add to train

* Update src/lerobot/envs/factory.py

Co-authored-by: Michel Aractingi <michel.aractingi@huggingface.co>
Signed-off-by: Jade Choghari <chogharijade@gmail.com>

* iterate on review

---------

Signed-off-by: Jade Choghari <chogharijade@gmail.com>
Co-authored-by: jade.choghari@huggingface.co <“chogharijade@gmail.com”>
Co-authored-by: Michel Aractingi <michel.aractingi@huggingface.co>

docs/source/_toctree.yml

@@ -63,6 +63,8 @@
     title: Implement your own processor
   - local: processors_robots_teleop
     title: Processors for Robots and Teleoperators
+  - local: env_processor
+    title: Environment Processors
   title: "Robot Processors"
 - sections:
   - local: so101