Add final unit tests

[RayStick]

Closes #

References #145

Proposed Changes

• Add final unit tests to get the package coverage up to scratch, as code cov is failing
• A few doc updates

Checklist for the author of this PR:

• [if package files were edited] I have run these checks locally:
  • devtools::document() to generates the .Rd files from any updated roxygen comments.
  • codemetar::write_codemeta() to ensures the metadata file is up to date.
  • styler::style_pkg() to ensure consistent code styling that match the guidelines.
  • devtools::check() for a comprehensive package check. I have resolved any warnings or errors, or written them here in the PR, for discussion.
• The code base and the documentation files match (they both reflect any recent changes).
• The title of this PR is clear and self-explantory.
• I have added any appropriate labels to this PR.
• This PR is now ready for review (and I have removed the draft PR status).