QC: Prep for gsm v2.1 release

QC Details

[x] Confirm that the version in the DESCRIPTION file is up to date.
[x] Run styler using the script from the style guide above (or by running gutil::style_code()) and commit any updates.
[x] Update NEWS.md with a summary of the revisions/additions in the release. Keep any information from previous releases to maintain traceability through versions.
[x] Ensure that the qualification specifications spreadsheet is up-to-date and accurate. If there have been any changes/updates to qualification tests, reach out to the qualification developer to update any necessary files.
[x] If applicable, review README.md and relevant vignettes to make sure updates are accurately described.
[x] Ensure all unit tests are passing.
[x] Check if all qualification tests are passing and if new features were added that need to be qualified. If updates are needed, they should be outlined in a release QC issue.
[x] Run devtools::spell_check() and resolve findings.
[x] Build site using pkgdown::build_site(). Check that all examples are displayed correctly and that all new functions occur on the Reference page.
[x] Open a clean R session. Run devtools::install() and then devtools::check() locally and confirm that there are no issues/conflicts.