fix: remove test artifacts and add coverage files to .gitignore

Co-authored-by: njzjz <9496702+njzjz@users.noreply.github.com>

Author: Copilot

.gitignore

@@ -51,7 +51,12 @@ buildcxx/
 node_modules/
 *.bib.original
 
+# Coverage files
+.coverage
+.coverage.*
+
 # Test output files (temporary)
 test_dp_test/
 test_dp_test_*.out
 *_detail.out
+out.json