Return sesolve when mesolve allows it

[albertomercurio]

Checklist

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Description

If the Hamiltonian is an Operator, the initial state is a Ket and the c_ops is Nothing, we can simplify the simulation of mesolve and directly call sesolve instead.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.27%. Comparing base (2b5e86e) to head (c0fe0b3).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #455   +/-   ##
=======================================
  Coverage   94.27%   94.27%           
=======================================
  Files          48       48           
  Lines        3022     3024    +2     
=======================================
+ Hits         2849     2851    +2     
  Misses        173      173           

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[ytdHuang]

The CUDA tests somehow fails, but I think it doesn't relate to our package