Add more robust error handling for the model construction

[jlperla]

The symbolic generation tools have very few checks to help debug model specification errors. These could be added as checks in the code with appropriate unit tests in https://github.com/HighDimensionalEconLab/DifferentiableStateSpaceModels.jl/blob/v0.4.19/test/make_perturbation_model.jl

The checks shoudl be added around https://github.com/HighDimensionalEconLab/DifferentiableStateSpaceModels.jl/blob/v0.4.19/src/make_perturbation_model.jl#L43-L55

Some ones that might be very helpful are:

• Ensure that p, y, x have no overlapping symbols
• Ensure that all uses of y and x are with the function notation so that the all_to_markov etc. will pass
• Ensure that there are no symbols in H that are not contained in y,x,p
• Ensure that there are no symbols in Γ, Ω, steady_states , steady_states_iv that are not contained in the p. I don't think that the y,x are allowed in those, but doublecheck.
• Make a few extra mistakes like having the wrong number of equations/etc. and see what the errors are.