Fix Windows build related to cppzmq

[jcfr]

Looking at CDash associated with both the Stable from 2025-02-16 (see here) and the Preview build from 2025-02-18 (see here), the extension is packaged and available on Linux and macOS but not on Windows.

Windows error are the following:

C:\path\to\SlicerJupyter-build\cppzmq\zmq.hpp(2506,12): error C3646: 'fd': unknown override specifier [C:\path\to\SlicerJupyter-build\xeus-build\xeus.vcxproj] [C:\D\P\S-0-E-b\SlicerJupyter-build\xeus.vcxproj]

(compiling source file '../xeus/src/xdap_tcp_client.cpp')
        C:\D\P\S-0-E-b\SlicerJupyter-build\cppzmq\zmq.hpp(2506,12):
        the template instantiation context (the oldest one first) is
            C:\D\P\S-0-E-b\SlicerJupyter-build\cppzmq\zmq.hpp(2502,41):
            while compiling class template 'zmq::poller_event'
    
C:\path\to\SlicerJupyter-build\cppzmq\zmq.hpp(2506,5): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int [C:\path\to\SlicerJupyter-build\xeus-build\xeus.vcxproj] [C:\D\P\S-0-E-b\SlicerJupyter-build\xeus.vcxproj]
    (compiling source file '../xeus/src/xdap_tcp_client.cpp')
    

For more details, see here