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/rss/feedbin.py

@@ -7,8 +7,8 @@ from my.config import feedbin as config
 from pathlib import Path
 from typing import Sequence
 
-from ..core.common import listify, get_files
-from ..core.compat import fromisoformat
+from my.core.common import listify, get_files
+from my.core.compat import fromisoformat
 from .common import Subscription
 
 
@@ -33,12 +33,10 @@ def parse_file(f: Path):
 from typing import Iterable
 from .common import SubscriptionState
 def states() -> Iterable[SubscriptionState]:
-    # meh
-    from dateutil.parser import isoparse
     for f in inputs():
         # TODO ugh. depends on my naming. not sure if useful?
         dts = f.stem.split('_')[-1]
-        dt = isoparse(dts)
+        dt = fromisoformat(dts)
         subs = parse_file(f)
         yield dt, subs