Output only text and move VTK to a post-processor

Problem

We can currently choose between text and VTK output. VTK output creates a visualization of tubes in 3D space that deform over time with arrays for pressure and flow rate. This visualization is nice but requires the user to choose the preferred post-processing method before running the simulation. Thus, there is only output possible, and it has to be known a priori. Furthermore, the input node*coord is currently mandatory but only required for VTK post-processing.

Solution

Remove VTK output from the solver and move it to a post-processor that can visualize text output in VTK.

Additional context

No response

Code of Conduct

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Start by tracing the solver's current text and VTK output paths, including where nodecoord is required. Then define the post-processor boundary and how it reads text output to produce the existing tube visualization with pressure and flow-rate arrays. Done means the solver emits text without requiring nodecoord, while a separate post-processor can recreate the VTK output.