Extend thrust::complex unit tests

To ensure a smooth transition from `thrust::complex` to `std::complex`,
the unit tests are extended. This approach will prevent unintended
constraints or extensions to `thrust::complex` functionality when the
the actual switch is done.

Key Enhancements:
- Introduce type-promoting operator tests.
- Generate distinct random values when multiple `thrust::complex` instances are used.
- Apply clang-format.

Author: Blonck