chore: add CI and CRAN-related files to .Rbuildignore

Co-authored-by: aider (anthropic/claude-sonnet-4-20250514) <aider@aider.chat>

Author: osorensen

.Rbuildignore

@@ -4,3 +4,8 @@
 ^data-raw$
 ^dev$
 ^\.github$
+^cran-comments\.md$
+^\.travis\.yml$
+^appveyor\.yml$
+^codecov\.yml$
+^\.covrignore$