core: cleanup deprecations, exclude from type checking and show runtime warnings

among affected things:

- core.common.assert_never
- core.common.cproperty
- core.common.isoparse
- core.common.mcachew
- core.common.the
- core.common.tzdatetime
- core.compat.sqlite_backup

my/location/gpslogger.py

@@ -27,7 +27,8 @@ from gpxpy.gpx import GPXXMLSyntaxException
 from more_itertools import unique_everseen
 
 from my.core import Stats, LazyLogger
-from my.core.common import get_files, mcachew
+from my.core.cachew import mcachew
+from my.core.common import get_files
 from .common import Location