Directly calculated growth

[sbfnk]

Description

This PR finishes splits out the direct growth rate calculation from #345 in order to make finishing that work more manageable. It was originally proposed in #213.

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 19b5707 is merged into main:

• ✔️default: 41.3s -> 34.2s [-44.04%, +9.41%]
• ✔️no_delays: 40.1s -> 39.4s [-11.29%, +7.68%]
• ✔️random_walk: 10s -> 9.73s [-15.96%, +10.57%]
• ✔️stationary: 19.8s -> 19.7s [-6.91%, +5.99%]
• ✔️uncertain: 52.1s -> 51.7s [-21.85%, +20.38%]
  Further explanation regarding interpretation and methodology can be found in the documentation.

[github-actions]

This is how benchmark results would change (along with a 95% confidence interval in relative change) if 19b5707 is merged into main:

• ✔️default: 32.5s -> 32.1s [-11.51%, +8.79%]
• ✔️no_delays: 38.5s -> 48.5s [-35.52%, +87.14%]
• ✔️random_walk: 10s -> 10.8s [-18.25%, +33.23%]
• ✔️stationary: 20.3s -> 24.8s [-41.81%, +86.83%]
• ✔️uncertain: 55.1s -> 56.6s [-12.59%, +17.87%]
  Further explanation regarding interpretation and methodology can be found in the documentation.

[github-actions]

This is how benchmark results would change (along with a 95% confidence interval in relative change) if 3b3b2a7 is merged into main:

• ✔️default: 38s -> 37.5s [-14.93%, +11.85%]
• ✔️no_delays: 44.7s -> 40s [-23.74%, +2.73%]
• ✔️random_walk: 10.8s -> 11.6s [-3.72%, +17.64%]
• ✔️stationary: 21.1s -> 21.4s [-10.32%, +12.34%]
• ✔️uncertain: 1.02m -> 57.4s [-34.97%, +21.53%]
  Further explanation regarding interpretation and methodology can be found in the documentation.

[github-actions]

This is how benchmark results would change (along with a 95% confidence interval in relative change) if 3b3b2a7 is merged into main:

• ✔️default: 37.1s -> 37.4s [-14.73%, +16.38%]
• ✔️no_delays: 41.9s -> 43.7s [-14.94%, +23.4%]
• ❗🐌random_walk: 10.1s -> 11.3s [+1.88%, +21.21%]
• ❗🐌stationary: 18.9s -> 21.2s [+1.9%, +22.6%]
• ✔️uncertain: 54.5s -> 53.3s [-20.16%, +15.89%]
  Further explanation regarding interpretation and methodology can be found in the documentation.

[seabbs]

Yup looks good. Just need a news file spelling update