Feature(#401): Add set.seed for short term trends

[atyrell3]

Justification

Short term trend plotting was not reproducible last year, resulting in trend lines appearing/disappearing when plots were regenerated. This is caused by the bootstrapping in the arfit methods used to fit the short-term trend.

Fixes #401

Types of changes

• Fix (non-breaking change which fixes a bug)
• Feature (non-breaking change which adds or changes functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Other change (if none of the other choices apply)

Reviewer instructions

• Reinstall package
• Run the same ecodata::plot_** call with n = 10 multiple times to ensure short-term trend (or lack thereof) is reproducible. Suggest to use plot_comdat(varName = "revenue", n = 10) as this gave us trouble last year.

Formatting

This repo contains an air.toml file that automatically formats code to a set of standards.
It is preferred that contributors and reviewers install the Air formatting tool.
Code submitted in this pull request will be automatically checked for correct formatting.

[BBeltz1]

this looks good, thanks abby! i'm not seeing any variation in the output of several runs of ecodata::plot_comdat(varName = "revenue", n = 10). the checks that are failing are expected and are unrelated to this change.

[andybeet]

thanks!