Allow for numeric imprecision for ordinal forecasts

[nikosbosse]

Description

This PR closes #996

As discussed in #996, this PR allows for some numeric imprecision when checking whether all probabilities sum to 1.

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]

Looks good. I think we might want to set it slightly bigger and potentially (though less sure) let the user specify it via an arg

[seabbs]

I simplified but otherwise this looks good to go