Introduce QobjEvo and use SciMLOperators for time evolution

[albertomercurio]

Description

With this PR I remove the obsolete operators like OperatorSum and TimeDependentOperatorSum, by introducing the QobjEvo operator, like in python. This struct takes advantage of the SciMLOperators.jl ecosystem, in order to handle in a lazy way complex operators like sum of them and time-dependent ones.

The ObjEvo is and AbstractQuantumObject, with the same fields as the QuantumObject, so they share many of the methods.

The introduction of using SciMLOperators.jl would push us towards the support of automatic differentiation of sesolve, mesolve and mcsolve, allowing the possibility to make quantum optimal control very efficiently.

I made this PR to improve the performance of complex SciMLOperators like our sum of time-dependent operators. So, we have to wait for a new release of the package first.

Todo list:

• Introduce QobjEvo operator
• Remove tlist from the parameters, and add it directly as argument
• Make TimeEvolutionSol type-stable
• replace t_l with a more readable tlist
• Update docstrings
• Remove OperatorSum and TimeDependentOperatorSum
• Update sesolve with the support to QobjEvo
• Update mesolve with the support to QobjEvo
• Update mcsolve with the support to QobjEvo
• Update ssesolve with support to QobjEvo
• Remove alg as argument for all the Problem functions
• Add tests for all the added methods
• Wait for merging of this PR and new release of SciMLOperators.jl

I will add the documentation in the next PRs. This one is already heavy.

[codecov]

Codecov Report

Attention: Patch coverage is 97.11538% with 12 lines in your changes missing coverage. Please review.

Project coverage is 93.80%. Comparing base (d3f1313) to head (deb2605).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/qobj/quantum_object_evo.jl	97.00%	3 Missing ⚠️
src/time_evolution/mesolve.jl	92.85%	2 Missing ⚠️
src/time_evolution/sesolve.jl	90.90%	2 Missing ⚠️
src/time_evolution/ssesolve.jl	96.00%	2 Missing ⚠️
src/qobj/quantum_object_base.jl	98.18%	1 Missing ⚠️
src/qobj/superoperators.jl	91.66%	1 Missing ⚠️
src/time_evolution/time_evolution_dynamical.jl	98.24%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #266      +/-   ##
==========================================
+ Coverage   93.41%   93.80%   +0.39%     
==========================================
  Files          31       32       +1     
  Lines        2337     2422      +85     
==========================================
+ Hits         2183     2272      +89     
+ Misses        154      150       -4     

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