nvtx3/nvtx3.hpp file not found for CPU-only build.

[Jacobfaib]

path/to/kvikio/cpp/include/kvikio/utils.hpp:28:10: fatal error: 'nvtx3/nvtx3.hpp' file not found
   28 | #include <nvtx3/nvtx3.hpp>
      |          ^~~~~~~~~~~~~~~~~

[Jacobfaib]

As a follow-up, ifdef-ing out the include then leads to

/path/to/kvikio/cpp/include/kvikio/posix_io.hpp:196:3: error: use of undeclared identifier 'nvtx3'
  196 |   KVIKIO_NVTX_FUNC_RANGE("posix_host_read()", size);
      |   ^