Remove _roi_ranges from SpectrumViewerWindowModel

[ashleymeigh2]

The _roi_ranges dictionary in SpectrumViewerWindowModel creates unnecessary complexity and synchronization issues with the SpectrumWidget's own ROI dictionary. Recent updates, such as enabling get_spectrum() to accept SensibleROI, have reduced the need for the model to maintain its own list of ROIs.

Desired Behaviour

The _roi_ranges attribute is fully removed, and all dependent methods are refactored out.

Current Behaviour

SpectrumViewerWindowModel maintains a _roi_ranges dictionary for mapping ROI names to ranges.
This requires constant synchronization with the ROI dictionary in SpectrumWidget, leading to redundancy and potential issues.

[ashleymeigh2]

COR and tilt docs further

[ashleymeigh2]

Remove _roi_ranges from SpectrumViewerWindowModel