Illustrate partialling errors of derived inputs in tt_function

[MImmesberger]

What problem do you want to solve?

This PR reproduces the partialling error of inputs that would be derived function in the tt_function. Its easiest to start with an example. Suppose:

• The policy_input is x_m
• You pass x_y as a scalar when requesting the tt_function
• Then, the tt_function will still ask for x_y as an input, i.e. the partialling that should have happened in step 2 did not happen

The reason is connected to the problems we had when building templates: Derived functions are not created when there is no input data to create them from. In particular, this line in with_processed_params_and_scalars is problematic, because there is no node x_y when creating the tt_function in the example above:

    for n, f in without_tree_logic_and_with_derived_functions.items():
        if n in processed_data:
             ... # This is where the partialling is prepared

From having a quick look at the code, it seems like it wouldn't break anything to carry over any scalar in the processed data through to with_partialled_params_and_scalars (i.e. not just those in without_tree_logic_and_with_derived_functions).