simplify version log message

[andy-beer]

Before refactoring each module tended to emit a debug message with a version string for the module. Given the huge number of modules after refactoring, the proposal here is that we remove all those debug messages and replace with a single one in the model.init.py module, indicating the resqpy version (ideally kept in sync with the major and minor elements of the release tags, at least).

The model._xml.py submodule can use the resqpy version from the init.py as the tail of the citation_format string, to avoid having to update the version in two places.

Individual modules may still have a static version attribute to aid interactive debugging.

[connortann]

I would recommend logging the actual resqpy version number, which is defined according to the git tags and release pipeline. This would be better than a static string - so far, these have been out of date most of the time.

The "true" version is already available as the dynamic module attribute resqpy.__version__. As a bonus, in a development setting the version string tells us the exact commit hash.