Split CNR visualization in two parts

## Feature Request

### Description

Split the visualization for CNR in two parts. One part is for signal visualization, one part for background visualization.

### Use cases

This improves performance for the interactive visualization, since only the part that changes on the input has to be reloaded.

### Possible implementation

Currently the visualization is a subplot. This can be changed to two single plots. The interactive visualization should be changed accordingly.

### Alternative solutions

Look for the CNR visualization code, likely in a plotting or visualization module. Identify the current subplot implementation and understand how signal and background are currently combined. Split into two separate plots and update any interactive visualization logic to handle them independently.

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