[FEATURE] - Add cleanup methods for static packages

Is your feature request related to a problem? Please describe.
We have nice cleanup methods for boundary condition packages, but not for static packages. This requires users now to come up with their own fixes.

Describe the solution you'd like

From the top of my mind:

DIS/DISV

1. Set idomain cells with thickness == 0 (or smaller than some tolerance limit) from 1 to -1
2. top needs to be masked with idomain > 0 of the first layer
3. bottom needs to be masked with a dataset that is shifted across the layer dim, so that underlying active cells still have a top

I'm not entirely sure about 1. and 2., as they can result in confusing results. idomain is normally treated in the codebase as the single source of truth. "Fixing" it is a bit dodgy.

NPF

1. Mask all k-values smaller than 0.0
2. Mask everything where idomain <= 0
3. Enforce icelltype as integer

I'm not so sure about 3, as it could result potentially in suprising results due to floating point precision errors.

STO

1. Mask everything where idomain <= 0

IC

1. Fill missing values with a laplace interpolation
2. Mask everything where idomain <= 0

Start by locating the existing cleanup methods for boundary-condition packages and the implementations of the DIS/DISV, NPF, STO, and IC packages. Review how idomain, layer shifts, masking, and missing values are currently handled. Done requires agreed cleanup behavior for each listed package, with tests covering the selected rules and their edge cases.