fix: address PR review comments for R language support

- Remove use of repo_path in tests, use relative paths instead
- Use os.path.join() for all path construction (Windows compatibility)
- Add _get_wait_time_for_cross_file_referencing() override (2.0 seconds)
- Remove all conditional checks in tests (no skipping)
- Remove accidentally committed Kotlin .gradle build artifacts
- Ensure all cross-file reference tests have proper assertions

All tests now pass on Linux/macOS/Windows. Addresses all review comments from @MischaPanch.

Author: drejom

src/solidlsp/language_servers/r_language_server.py

@@ -19,6 +19,10 @@
 class RLanguageServer(SolidLanguageServer):
     """R Language Server implementation using the languageserver R package."""
 
+    @override
+    def _get_wait_time_for_cross_file_referencing(self) -> float:
+        return 2.0  # Increase wait time for R language server cross-file referencing
+
     @override
     def is_ignored_dirname(self, dirname: str) -> bool:
         # For R projects, ignore common directories