expose MMCore_version variables in MMCore.h

[tlambert03]

The MMCore version info is only declared in MMCore.cpp, making it a bit harder to access in bindings like pymmcore. (you have to resort to manually declaring it which is error prone. this exposes those variables in the public header

[marktsuchida]

Is the goal to make it easier to access the version at run time from Python? If so we might consider a variant of CMMCore::getVersionInfo() that returns 3 numbers instead of a string. That can be a static member function (or even a free function) so that CMMCore need not be instantiated. I think this is better than exposing integer constants; something like

static void CMMCore::getVersion(int& major, int& minor, int& patch);

(As you know the pymmcore version number has a manually incremented "packaging" version (5th element) that is specific to pymmcore; also the manually updated version is tested for match with getVersionInfo().)

[tlambert03]

it's about compile time, rather than runtime. this would enable:

https://github.com/pymmcore-plus/pymmcore-nano/blob/46fa1769ec4bdedb251d62c042135ca3adc61205/src/_pymmcore_nano.cc#L244-L245

...which removes the need to manually increment packaging info and avoids any possibility of the two going out of sync (i.e. it doesn't depend on pytest to catch it)