[Major] Major change in gym's space

[anthony0727]

Gym's rules regarding space has been strengthened

e.g.

gym==0.24 requires observation to be ONLY np.array

and, since gym==0.20 observation_space's attribute is protected(can not be set lazily)

rules regarding >=0.24 will be merge in next PR

[anthony0727]

@leeynsn @Moong1234 regarding Graph obs,

Since gym's convention is VERY popular practice among the RL community

We should stick to this

Otherwise, those who wish to use other RL libraries with marlenv, they can't

[anthony0727]

Will simply disable env checking for now,

https://github.com/openai/gym/blob/94081fbc0ade19747c9eea8aa435310f46971873/gym/envs/registration.py#L521

https://github.com/openai/gym/blob/979407f4c4aef3bebba6f317a6495ab2a6fc359c/gym/wrappers/env_checker.py#L15

[anthony0727]

issue with grid obs is resolved with

commit : 2ee67b7