Unable to set the environment seed

[NishanthVAnand]

Describe the bug
I get NotImplementedError when I try to set seed on some of the envrionments.

To Reproduce

env = PuddleWorld()
env.seed(seed)

Expected behavior
I expected seed to be set

System information (please complete the following information):

• OS: macOS Big Sur 11.6
• Python version Python3.8.6
• Mushroom version 1.7.0

Additional context
Error message I get

File  "/python3.8/site-packages/mushroom_rl/core/environment.py", line 137, in seed
     raise NotImplementedError
 NotImplementedError

[boris-il-forte]

The seed function was designed to interface with Gym environments that may require setting a seed.
Every mushroom environment uses the default NumPy random seed generator.
Probably, it's a good idea to add a more informative message in the agent class or to set the NumPy seed there.
However, we prefer to set the random seed in the experiment function explicitly, before creating the environment. This is due to the fact that the same seed will affect both the environment and the policy (unless using a torch policy, in which case, also the torch seed must be set).

[boris-il-forte]

Fixed in the latest commit. Now the method warns you, pointing to the correct solution instead of crashing.