imported Disc, EOM, and Model to init file

[HYP3R00T]

In the RTD doc, inside Running section, the sample code is not working. The reason is that in the first line when we are import, it is not working. Instead of that, the solution we have is to do the following.

from frispy.disc import Disc

So, to ensure the given sample working fine. I have modified the __init__.py file a bit.

Also, the poetry.lock file is outdate, so I generated a new one.

[HYP3R00T]

added import in __init__.py to allow user to directly import Disc, EOM and Model classes