Allow runtime evaluation also on multiple cores

[zweihuehner]

Currently, runtime evaluation only works for single-core simulations. When running on multiple cores, the output files are split across cores and need to be reconstructed for evaluation.

Required updates in the mikesimulation module:

1. Implement reconstruct_output()

• Input: Simulation output files from SimObsPairCollection
• Collects output files from all cores
• Stitches the split files together at every x-th timestep
• Produces a single merged output file with the name as given in the SimObsPairCollection

2. Integrate reconstruct_output() in _run_process()

• Call reconstruct_output() before simobs.update()
• Ensures a complete dataset is available for runtime evaluation

[zweihuehner]

Possible ideas to reconstruct:

• mikeio: https://github.com/DHI/mikeio/blob/main/notebooks/Dfsu%20-%20Merge%20subdomain%20files.ipynb. Ask IOKO
• Generic MikeZero functionality. This is probably more mature. Ask SLE