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/emfit/__init__.py

@@ -21,8 +21,7 @@ from my.core import (
     Res,
     Stats,
 )
-from my.core.common import mcachew
-from my.core.cachew import cache_dir
+from my.core.cachew import cache_dir, mcachew
 from my.core.error import set_error_datetime, extract_error_datetime
 from my.core.pandas import DataFrameT