Issue #925 - Remove function interval_coverage_deviation()

[nikosbosse]

Description

This PR closes #925.

As discussed by me, with myself, after changing my opinion multiple times: This PR simply removes the function interval_coverage_deviation().

Users can still access its output using get_coverage() if they want - but as a standalone metric it's not that useful.

Checklist

• My PR is based on a package issue and I have explicitly linked it.
• I have included the target issue or issues in the PR title as follows: issue-number: PR title
• I have tested my changes locally.
• I have added or updated unit tests where necessary.
• I have updated the documentation if required.
• I have built the package locally and run rebuilt docs using roxygen2.
• My code follows the established coding standards and I have run lintr::lint_package() to check for style issues introduced by my changes.
• I have added a news item linked to this PR.
• I have reviewed CI checks for this PR and addressed them as far as I am able.

[seabbs]

And as discussed on slack. Good idea. Looks good.