Segment: Include <memory> so we don't get error at compile time
Example build failure:
In file included from /home/paul/sigrok-util/cross-compile/mingw/build_release_64/pulseview/pv/data/segment.cpp:21:
/home/paul/sigrok-util/cross-compile/mingw/build_release_64/pulseview/pv/data/segment.hpp:130:14: error: 'shared_ptr' in namespace 'std' does not name a template type
130 | typedef std::shared_ptr<pv::data::Segment> SharedPtrToSegment;
| ^~~~~~~~~~
/home/paul/sigrok-util/cross-compile/mingw/build_release_64/pulseview/pv/data/segment.hpp:32:1: note: 'std::shared_ptr' is defined in header '<memory>'; did you forget to '#include <memory>'?
31 | #include <QObject>
+++ |+#include <memory>
32 |