EpisodeData len overload

[Tezirg]

In any version, getting the length of an Episode loaded from disk crashes:

from grid2op.Episode import EpisodeData

logs_path = "./my_runner_output_dir"
episode_id = "0001" 
episode_data = EpisodeData.from_disk(agent_path=logs_path, name=episode_id)
n_steps = len(episode_data)

Overloading __len__ should return an integer type. Instead we have the following:

TypeError: 'str' object cannot be interpreted as an integer

[BDonnot]

Fixed in version v0.8.1