First quick pass to make refactoring QuTiP code → jaxquantum code easier

[Phionx]

This is a first, low-effort pass at making it easier to move from qutip to jaxquantum.

Some issues already identified:

• Add an identity operator constructor with the same name
• make it easier to create Qarray's (or add warnings if not possible) / maybe also define Qobj as Qarray

@shoumikdc @GabrieleRolleri and Max Hays please add to this list

[shoumikdc]

Also:

• Add expectation value calculations into sesolve and mesolve (e_ops)

And potentially:

• Auto convert qutip objects to jqt Qarrays so that people could in principle pass in Qobjs to their functions

[Phionx]

Also:

• Add expectation value calculations into sesolve and mesolve (e_ops)

Yup, tracked by #19

And potentially:

• Auto convert qutip objects to jqt Qarrays so that people could in principle pass in Qobjs to their functions

I don't want to handle Qobjs conversions automatically within jaxquantum, but I can see jqt.Qobj being another name for jqt.Qarray to make code refactoring easier