Fix Framestack obs env_checker

[corentinlger]

Fix env_checker function for gymnasium FrameStacked observations (previously raised an error)

Description

FrameStacked obs from Gymnasium only support Box obs and are stored in a LazyFrames class. Because the associated obs_space is a np.ndarray, I only added a condition where I still check if the obs is a np.ndarray class, but also a LazyFrames class (when _is_numpy_array_space is True).

@qgallouedec also proposed to use np.can_cast which worked, but the type hinting for the function became really long (and could lead to errors) because you can also cast str, bytes ... So I don't know if the solution used here is the best but it seems to work. What do you think about it ?

Motivation and Context

Solves the problem mentionned in this issue.

closes #1500

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Types of changes

• [x ] Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation (update in the documentation)

Checklist

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• My change requires a change to the documentation.
• [ x] I have updated the tests accordingly (required for a bug fix or a new feature).
• [ x] I have updated the documentation accordingly.
• I have opened an associated PR on the SB3-Contrib repository (if necessary)
• I have opened an associated PR on the RL-Zoo3 repository (if necessary)
• [x ] I have reformatted the code using make format (required)
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[qgallouedec]

Thank you @corentinlger!

Are we sure that everything is working with an environment that returns LazyFrame?

[qgallouedec]

but the type hinting for the function became really long (and could lead to errors) because you can also cast str, bytes

Where do you need to update the type hint?

[corentinlger]

Yes I checked with several FrameStacked envs that returned LazyFrames observations and everything worked !

If I am not wrong, when using np.can_cast I needed to update the type hint on the 'check_obs' function. When I ran make pytype I got this error :

'''
stable_baselines3/common/env_checker.py:190: error: Argument 1 to "can_cast" has incompatible type "Union[Tuple[Any, ...], Dict[Any, Any], ndarray[Any, Any], int]"; expected "Union[Union[_SupportsArray[dtype[Any]], _NestedSequence[_SupportsArray[dtype[Any]]], bool, int, float, complex, str, bytes, _NestedSequence[Union[bool, int, float, complex, str, bytes]]], Union[dtype[Any], None, Type[Any], _SupportsDType[dtype[Any]], str, Union[Tuple[Any, int], Tuple[Any, Union[SupportsIndex, Sequence[SupportsIndex]]], List[Any], _DTypeDict, Tuple[Any, Any]]]]" [arg-type] Found 1 error in 1 file (checked 82 source files) make: *** [Makefile:11: mypy] Error 1
'''

With the other option I just added LazyFrames to the obs type hint as follows : "obs: Union[tuple, dict, np.ndarray, int, LazyFrames]" and it worked.

Do you think there is a better way to solve the problem ?