[WIP] Observer Pattern for UpdateState

[henrij22]

This is to be merged in Nonlinear EAS PR

I ve now got working code with https://godbolt.org/z/b9cM5e714
I implemented Broadcasters next to Observers, so there are both implementations right now.

OLD

I don't know how to get this to work without a major overhaul of the observer thing.
The problem is that i want to notify like

      this->notify(NonLinearSolverMessages::CORRECTION_UPDATED, x, correction_);

So now the problem is that x and correction can have a lot of different types, Eigen Vector, Matrices, SparseVectors ...
For that i subclassed IOObservable like

template <typename MessageType, typename VectorType = Eigen::VectorX<double>,
          typename VectorType2 = Eigen::VectorX<double>>
class IObservable

that works now if

void IObservable<MT, VT1, VT2>::notify(MT message, const VT1& vec, const VT2& dx) {
  auto vectorOfObserversOfASpecificMessage = observers_[message];
  for (auto&& obs : vectorOfObserversOfASpecificMessage)
    obs->update(message, vec, dx);
}

has an observer that is also templated with two vectors

template <typename MT, typename VectorType = Eigen::VectorX<double>, typename VectorType2 = Eigen::VectorX<double>>
class IObserver

virtual void updateImpl([[maybe_unused]] MessageType message, [[maybe_unused]] const VectorType& vec,
                          [[maybe_unused]] const VectorType2& dx) {}

for example like

class NewtonRaphson : public IObservable<NonLinearSolverMessages, typename NLO::DerivativeType, typename NLO::ValueType>

but that means that every observer has to be templated like that because we need in IOObservable

  using ObserverVector = std::vector<std::shared_ptr<IObserver<MessageType, VectorType, VectorType2>>>;
  using ObserverMap    = std::map<MessageType, ObserverVector>;

which then means that every derived class of IOObserver somehow needs to be convertable to that.
Now i have a problem:

  auto nonLinearSolverObserver = std::make_shared<NonLinearSolverLogger>();
  nr->subscribeAll(nonLinearSolverObserver);  

doenst work because of

no known conversion from 'shared_ptr<_NonArray<NonLinearSolverLogger>>' to 'shared_ptr<IObserver<NonLinearSolverMessages, Matrix<double, -1, -1, 0, -1, -1>, Matrix<double, -1, 1, 0, -1, 1>>>' for 1st argument
[build]   void subscribeAll(std::shared_ptr<IObserver<MessageType, VectorType, VectorType2>> observer);

So i don't really know how to convert this because

  void subscribeAll(std::shared_ptr<IObserver<MessageType, VectorType, VectorType2>> observer);

takes a shared ptr to some observer with these template arguments.

Maybe you have a good idea @tarun-mitruka @rath3t

Maybe this can work out
#260

[codecov]

Codecov Report

Attention: Patch coverage is 77.27273% with 20 lines in your changes missing coverage. Please review.

Project coverage is 81.29%. Comparing base (acb6da3) to head (9e839cb).

Files with missing lines	Patch %	Lines
ikarus/controlroutines/pathfollowing.inl	0.00%	10 Missing ⚠️
...olver/newtonraphsonwithscalarsubsidiaryfunction.hh	0.00%	8 Missing ⚠️
ikarus/utils/broadcaster/broadcaster.hh	75.00%	2 Missing ⚠️

Additional details and impacted files

@@               Coverage Diff                @@
##           NonlinearEAS     #346      +/-   ##
================================================
+ Coverage         80.72%   81.29%   +0.56%     
================================================
  Files                70       68       -2     
  Lines              2309     2299      -10     
================================================
+ Hits               1864     1869       +5     
+ Misses              445      430      -15     

Flag	Coverage Δ
tests	81.29% <77.27%> (+0.56%)	⬆️

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