Quantum gate models for IR integration

[thisac]

Context:
An abstraction for quantum gates can be useful for building a Jet interpreter for XIR scripts if it supports converting a unitary matrix into a Tensor instance.

Description of the Change:

• The jet Python package now includes a base Gate class for modelling quantum gates.
• A number of derived Gate classes for modelling CV and qubit gates are now available.
• The data type factory methods in __init__.py have been moved to a separate factory.py module.

Benefits:

• It is trivial to model quantum gates with the jet package and convert them into Tensor objects.

Possible Drawbacks:
None.

Related GitHub Issues:
None.

[Mandrenkov]

Thanks for the review, @josh146! Let me know what you think of the changes.

[mlxd]

Excellent work here. I think it can be left for now, but at some later date I'd love to see |0><0| and |1><1| projectors, as well as controlled arbitrary (non-)unitary gates. Though, I think what you have here looks great, and I'm happy to see it go in!

[josh146]

Thanks @Mandrenkov!

[antalszava]

Overall this looks like an amazing addition! 😍 🚀

For improvement (maybe in a subsequent PR even), the docstrings could be adjusted to adhere to convention. Was also curious about each CV gate getting a dedicated cutoff value, not sure if this can be easily kept track of for the entire tensor network (maybe missing something).