feat(specs): make environment specs managed attributes

[aar65537]

closes #98

• Implements private _*_spec properties on the Environment class. The properties are accessed through *_spec managed attributes implemented with the @property decorator. Properties are initialized with _make_*_spec() methods during Environment initialization.
• Implements generic ActionSpec type on the Environment class in order to statically type the action_spec attribute.
• Updates all environments to conform with changes to Environment class.
• Implements unit tests to ensure Environment specs can be accessed from a jitted function.
• Changes all references to *_spec() method to *_spec attribute.

Edit:
now also closes #221

• Implements generic Observation type on Environment
• Implements generic types on Wrapper classes, so that Wrappers will inherit type hints from the Environments they wrap

[clement-bonnet]

Thank you @aar65537 for the contribution, it is a great improvement to the library! I just have one comment regarding the ActionSpec which I think we should not have.
Please let me know what you think!

[sash-a]

Sorry for the radio silence, I still want to get this in! What do you think about using cached_properties instead of properties as the spec should never change?

[aar65537]

I think cached_properties should work. The only issue I foresee is you might have to access the properties in the __init__ method to ensure the arrays are initialized outside of a jitted function.

[sash-a]

I think cached_properties should work. The only issue I foresee is you might have to access the properties in the __init__ method to ensure the arrays are initialized outside of a jitted function.

True, but we know what the cached properties are, so we could call them in the base env classes init?

[sash-a]

Also just a heads up, we're making a push to get sliding tile puzzle and flatpack envs merged before the ICLR camera ready deadline (about a week). Once this is done we'll get to this PR 😄

[aar65537]

Thanks for the heads up. I changed all of the environments to use cached_property. I think it is more succinct than my original implementation. Thank you for the suggestion.

[sash-a]

Thanks for this @aar65537, really nice change 😄

[clement-bonnet]

All good to me! Except that we are missing changes for at least SlidingTilePuzzle since we merged it. Could we possibly port these specs changes to that 22nd environment as well, please?

[aar65537]

I've implemented the changes for the SlidingTilePuzzle and cleaned up the last references to action_spec() in the docs. That should be all the environments.