CUDA build warnings

[rhornung67]

When attempting to build the develop branch using our host config files to configure for llvm@19.1.3_cuda(matrix and rzvector yield the same results), several compiler warnings and errors are encountered. Before the build dies:

• warnings: unused variables and variables used before initialization in thirdparty/tests
• warnings: calling constexpr __host__ function from __host__ __device function in core/detail/FlatTable.hpp, core/FlatMapUtil.hpp. Resolve by removing __host__ decoration from constexpr function or use experimental flag --expt-relaxed-constexpr?
• warnings: similar to above in core/tests/core_array_for_all.hpp
• warnings: similar to above in primal/geometry/Polygon.hpp, primal/geometry/BoundingBox.hpp, and primal/geometry/Vector.hpp
• warnings: similar to above in primal/detail/clip_impl.hpp
• There may be other warnings to address as well.

[rhornung67]

From @adayton1 "This flag is the one I asked the nvidia folks about and they said that they plan to support it for the foreseeable future. It is less experimental and more of an indication that just because a function is constexpr doesn't mean it is necessarily device safe (e.g. if it uses host memory). But I think the vast majority of constexpr functions should be safe to use on the device."

This flag refers to the nvcc compiler flag --expt-relaxed-constexpr

[kennyweiss]

@BradWhitlock mentioned that it might be difficult to fix the warnings on the primal primitives since they are using axom::Array and will be difficult to properly use on the GPU. We'd need to rethink the storage for these, e.g. in the way that primal::Polygon take a storage parameter.