[FEA]: Debugger pretty-printers: `cuda::std::optional`

Create a `lldb` and `gdb` pretty printer for `cuda::std::optional`.

The printer should live under `libcudacxx/share/libcudacxx//optional.py` for each debugger.

In addition, the pretty printers should be exhaustively tested, with tests living under `libcudacxx/test/debugging/optional`. See the existing tests in that directory for inspiration.

Read the existing tests under libcudacxx/test/debugging/optional and use them as the model for coverage. Add the lldb and gdb printers under libcudacxx/share/libcudacxx//optional.py, then extend the optional tests until both printers are exhaustively tested.

Written by the indexing model from the issue text.