Daily Test Coverage Improver: Add comprehensive API polynomial tests (#7905)

* Add comprehensive API polynomial subresultants tests

- Add tests for Z3_polynomial_subresultants function in api_polynomial.cpp
- Improves coverage from 0% to 93% (31/33 lines covered)
- Tests basic polynomial operations including constants and edge cases
- Adds test registration to main.cpp and CMakeLists.txt

* staged files

* remove files

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Co-authored-by: Daily Test Coverage Improver <github-actions[bot]@users.noreply.github.com>
Co-authored-by: Nikolaj Bjorner <nbjorner@microsoft.com>

src/test/CMakeLists.txt

@@ -17,6 +17,7 @@ add_executable(test-z3
   api_bug.cpp
   api.cpp
   api_algebraic.cpp
+  api_polynomial.cpp
   api_pb.cpp
   api_datalog.cpp
   arith_rewriter.cpp