Tests for PID controlled pump

[SouthEndMusic]

New cases for PID control to be tested emerged due to refactoring (#474, #465). These test cases are:

• The PID controlled pump flowing out into FractionalFlow nodes;
• The PID controlled basin influencing itself trough being connected to e.g. a LinearResistance. This could be added to the equation test by connecting a LevelBoundary via LinearResistance to the PID controlled basin. This was first trought to be hard to support (Stricter PID connectivity validation #481) but it seems to be supported now;
• The PID controlled basin getting in the 'reduction factor regime' (although this is probably quite rare in practice).
• Upstream of the PID controlled weir is a LevelBoundary node (done in Add weir #485).

[SouthEndMusic]

Regarding the test of the controlled pump flowing out into fractional flow nodes: this possibility is also not covered yet in

function update_jac_prototype!(
    jac_prototype::SparseMatrixCSC{Float64, Int64},
    p::Parameters,
    node::PidControl,
)::Nothing

[SouthEndMusic]

Regarding the following:

The PID controlled basin influencing itself trough being connected to e.g. a LinearResistance

In order to do this, the $\frac{\partial E}{\partial u_i}$ (see equations.qmd in #485) are needed. Most of these are $0$; a nice method has to be found to figure out which aren't (currently they aren't incorporated at all).

[visr]

Paused this for now, we'll probably work on #152 first. Until then jac = false can be used for any models for which the Jacobian is not complete.