Support for solution derivative functions

Hi,

I am using this library in a setting where I want to use the solution derivative functions provided by OSQP (like `osqp_adjoint_derivative_compute`). As far as I can tell, this library does not provide an interface for those functions - would it be possible to add that?

Thanks!

Start by reviewing the existing osqp-eigen interfaces and the OSQP solution derivative functions, including osqp_adjoint_derivative_compute. Define the wrapper surface needed for these functions and verify that the exposed interface supports the requested derivative workflow.

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