build: keep stray Rplots.pdf out of the build tarball

[ehrlinger]

Summary

Add Rplots\.pdf$ to .Rbuildignore so a stray Rplots.pdf never gets bundled into the build tarball.

Why

devtools::check / run_examples execute the \donttest gg_* examples, which end in plot(...) and auto-print to the default graphics device, leaving tests/testthat/Rplots.pdf. It's already in .gitignore (never committed), but R CMD build uses .Rbuildignore — which didn't exclude it — so a local build picked up the ~6.9 MB stray and inflated the tarball. No test creates it (verified across the suite under both default and NOT_CRAN=true); it's purely an example-execution artifact.

This is preventative build hygiene — no package code or behaviour change.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.15%. Comparing base (bfef645) to head (98a5e55).

Additional details and impacted files

@@           Coverage Diff           @@
##              dev     #107   +/-   ##
=======================================
  Coverage   87.15%   87.15%           
=======================================
  Files          46       46           
  Lines        4016     4016           
=======================================
  Hits         3500     3500           
  Misses        516      516           

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[Copilot]

Pull request overview

This PR updates the package build ignore rules to prevent accidental inclusion of a locally generated Rplots.pdf artifact in R CMD build tarballs, keeping build outputs stable and appropriately sized.

Changes:

• Add an .Rbuildignore rule for Rplots\.pdf$ so example/test plotting artifacts aren’t bundled into the source tarball.
• Document the rationale with inline comments (noting it’s already covered by .gitignore).

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