fix_dist -> fix_parameters

[sbfnk]

Description

This PR closes #715.

Initial submission checklist

• My PR is based on a package issue and I have explicitly linked it.
• I have tested my changes locally (using devtools::test() and devtools::check()).
• I have added or updated unit tests where necessary.
• I have updated the documentation if required and rebuilt docs if yes (using devtools::document()).
• I have followed the established coding standards (and checked using lintr::lint_package()).
• I have added a news item linked to this PR.

After the initial Pull Request

• I have reviewed Checks for this PR and addressed any issues as far as I am able.

[github-actions]

This is how benchmark results would change (along with a 95% confidence interval in relative change) if 81258af is merged into main:

• ✔️default: 33.9s -> 35.3s [-14.92%, +23.37%]
• ✔️no_delays: 39.9s -> 43.7s [-10.59%, +29.37%]
• ✔️random_walk: 10.4s -> 9.96s [-11.72%, +2.77%]
• ✔️stationary: 19.6s -> 19.3s [-13.01%, +9.43%]
• ✔️uncertain: 53.8s -> 52.2s [-21.96%, +15.89%]
  Further explanation regarding interpretation and methodology can be found in the documentation.

[jamesmbaazam]

Thanks. You could also add a test for deprecation of fix_dist().

[jamesmbaazam]

All looks good to me.

[sbfnk]

@jamesmbaazam can you still approve this now that you've co-authored? If not we might need @seabbs's help to allow this to be merged.

[jamesmbaazam]

Is the touchstone failure being fixed by any of you? @seabbs @sbfnk