Drop namespace std

[penguinpee]

Solve build error when compiling with GCC 15.

[penguinpee]

Compiling the Python module with GCC 15 resulted in:

  /builddir/build/BUILD/dlib-19.24.8-build/dlib-19.24.8/tools/python/src/sequence_segmenter.cpp:100:5: error: reference to ‘ranges’ is ambiguous
    100 |     ranges segment_sequence_dense (
        |     ^~~~~~
  In file included from /builddir/build/BUILD/dlib-19.24.8-build/dlib-19.24.8/dlib/../dlib/matrix/../fft/fft_size.h:6,
                   from /builddir/build/BUILD/dlib-19.24.8-build/dlib-19.24.8/dlib/../dlib/matrix/../fft/fft.h:7,
                   from /builddir/build/BUILD/dlib-19.24.8-build/dlib-19.24.8/dlib/../dlib/matrix/matrix_fft.h:11,
                   from /builddir/build/BUILD/dlib-19.24.8-build/dlib-19.24.8/dlib/../dlib/matrix/matrix_conv.h:8,
                   from /builddir/build/BUILD/dlib-19.24.8-build/dlib-19.24.8/dlib/../dlib/matrix.h:13,
                   from /builddir/build/BUILD/dlib-19.24.8-build/dlib-19.24.8/dlib/../dlib/python/numpy_image.h:8,
                   from /builddir/build/BUILD/dlib-19.24.8-build/dlib-19.24.8/dlib/../dlib/python.h:9,
                   from /builddir/build/BUILD/dlib-19.24.8-build/dlib-19.24.8/tools/python/src/opaque_types.h:6,
                   from /builddir/build/BUILD/dlib-19.24.8-build/dlib-19.24.8/tools/python/src/sequence_segmenter.cpp:4:
  /usr/include/c++/15/numeric:735:11: note: candidates are: ‘namespace std::ranges { }’
    735 | namespace ranges
        |           ^~~~~~
  /builddir/build/BUILD/dlib-19.24.8-build/dlib-19.24.8/tools/python/src/sequence_segmenter.cpp:15:63: note:                 ‘typedef class std::vector<std::pair<long unsigned int, long unsigned int> > ranges’
     15 | typedef std::vector<std::pair<unsigned long, unsigned long> > ranges;
        |                                                               ^~~~~~
  /builddir/build/BUILD/dlib-19.24.8-build/dlib-19.24.8/tools/python/src/sequence_segmenter.cpp:118:5: error: reference to ‘ranges’ is ambiguous
    118 |     ranges segment_sequence_sparse (
        |     ^~~~~~

The referenced candidate namespace std::ranges { } was introduced in <numeric> in GCC 15. It was not part of GCC 14, though upstream considers backporting.

[penguinpee]

Having looked a bit closer at the other source files in tools/python/src, the issue could also be solved with the approach used in matrix.cpp. That is including <dlib/string.h> and replacing using namespace std; with using std::string; and using std::ostringstream;.

I'm open to suggestions (not a C/C++ expert, nor very familiar with the code base).

[davisking]

Thanks for the PR :D

What you did is a fine way to deal with the issue.