`KeyDoor`: the door can spawn on the room wall

[epignatelli]

import matplotlib.pyplot as plt
import navix as nx
import jax

env = nx.environments.KeyDoor(12, 6, 100, observation_fn=nx.observations.rgb)

key = jax.random.PRNGKey(0)
timestep = env.reset(key)
plt.imshow(timestep.observation)
plt.show()