[Feature Request] Gym tuple space mapping

Motivation

TorchRL cannot handle environments with gymnasium.spaces.Tuple observation spaces. I think these are fairly common outside of MuJoCo/Atari envs.

Solution

Support for tuple spaces

Additional context

Traceback (most recent call last):
  File "/Users/smorad/code/rqdn/segment_dqn.py", line 92, in <module>
    GymWrapper(load_popgym_env(config), device=device),
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/smorad/code/from_src/torchrl/torchrl/envs/libs/gym.py", line 371, in __init__
    super().__init__(**kwargs)
  File "/Users/smorad/code/from_src/torchrl/torchrl/envs/common.py", line 1388, in __init__
    self._make_specs(self._env)  # writes the self._env attribute
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/smorad/code/from_src/torchrl/torchrl/envs/libs/gym.py", line 522, in _make_specs
    observation_spec = _gym_to_torchrl_spec_transform(
                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/smorad/code/from_src/torchrl/torchrl/envs/libs/gym.py", line 192, in _gym_to_torchrl_spec_transform
    raise NotImplementedError("gym.spaces.tuple.Tuple mapping not yet implemented")
NotImplementedError: gym.spaces.tuple.Tuple mapping not yet implemented

Checklist

• I have checked that there is no similar issue in the repo (required)