Add unit tests for derivative computation

[imciner2]

Now that the derivative computation has been merged into the develop-1.0 branch, we need to add C-based unit tests for it to ensure the future changes to it don't break things. These can be based off of the Python tests (and can even call the necessary Python libraries to compute the derivatives when generating the testset.

We should ensure the derivative tests include the following cases at a minimum:

• [ ] Generic QP
• [ ] Unconstrained QP
• [ ] Equality constrained QP
• [ ] Inequality constrained QP
• [ ] LP