[syahra712]

Fixes #5369

The CRAN DESCRIPTION parser now:

• splits Depends on every comma, so R (>= 3.4.0), methods, utils gives three dependencies (R with >= 3.4.0, methods, utils with >= 3.0) instead of one R dependency with a garbled requirement;
• skips empty entries, so a file with no Depends field returns no dependencies instead of raising ValueError: Invalid purl;
• returns (None, None) from get_party_info for an empty value, so a file without Author or Maintainer (common in source packages that only have Authors@R) no longer raises TypeError.

Tests: two new fixtures (cran/single-line-depends, cran/no-depends) and a unit test for the new get_dependencies helper. All three tests fail on develop and pass with this change. The existing codetools and geometry expectations are unchanged.

Tasks

• Reviewed contribution guidelines
• PR is descriptively titled 📑 and links the original issue above 🔗
• Tests pass -- pytest tests/packagedcode/test_cran.py (5 passed)
• Commits are in uniquely-named feature branch and has no merge conflicts 📁
• Updated documentation pages (if applicable)
• Updated CHANGELOG.rst (if applicable)