Fix ROI movement not updating spectrum unless selected

[ashleymeigh2]

Issue Closes #2486

Description

• Fixed an issue where moving an ROI did not update the spectrum plot unless the ROI was selected first.
• roi_changed signal now correctly emits the SpectrumROI object instead of an ROI or string.
• Updated handle_roi_moved to process only the moved ROI for efficiency.
• Ensured remove_roi correctly retrieves and passes the SpectrumROI object to the presenter.

Developer Testing

• I have verified unit tests pass locally: python -m pytest -vs
• Manually tested by:
  • Adding an ROI and moving it.
  • Checking that the spectrum updates immediately without needing selection.
  • Removing an ROI and verifying spectrum updates correctly.

Acceptance Criteria and Reviewer Testing

• Unit tests pass locally: python -m pytest -vs
• Adding a new ROI updates the spectrum on resize.
• Moving an existing ROI updates the spectrum in real-time.
• Removing an ROI updates the spectrum correctly.

Documentation and Additional Notes

[samtygier-stfc]

I'll rebase this to deal with any conflicts with other PRs. Also I'll take the sigRegionChanged connection back out, because that was done for #2155

[coveralls]

coverage: 72.891% (+0.02%) from 72.872%
when pulling ed0a65f on 2486_spec_plot_update
into 34d5abd on main.

[samtygier-stfc]

I also made some tweaks to the remove ROI code, as pop() taking the ROI out of spectrum_widget.roi_dict prevent it being removed from the image view. And removed some bits that were tolerating missing things in dictionaries.