Add a method for tensor product of cudaq::states and a method to take trace of cudaq::state (C++)

[YauheniTalochkaN]

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Describe the feature

Dear developers,

Could you please add a method for tensor product in CUDA-Q (C++) if it is not already there?
It allows us to easily build a density matrix using a certain state vector and to build, for instance, using two density matrices, an extended matrix of the total system consisting of two subsystems.
Moreover, could you please add a method to take a trace of a cudaq::state if it is a density matrix?

[YauheniTalochkaN]

It would also be nice if you provided a C++ description of these examples, especially for the density matrix.

[sacpis]

It would also be nice if you provided a C++ description of these examples, especially for the density matrix.

Hi @YauheniTalochkaN, We have added C++ examples for dynamics along with description. Checking if there is any issue with the CI now.

[YauheniTalochkaN]

Dear @sacpis, I see the C++ examples on this page, but don't see others here. These pages contain different examples, as I can see. In particular, the second page has codes concerning the density matrix.