core.common: move listify to core.utils.itertools, use better typing annotations for it

also some minor refactoring of my.rss

my/rss/all.py

@@ -1,6 +1,7 @@
 '''
 Unified RSS data, merged from different services I used historically
 '''
+
 # NOTE: you can comment out the sources you're not using
 from . import feedbin, feedly
 
@@ -12,5 +13,5 @@ def subscriptions() -> Iterable[Subscription]:
     # TODO google reader?
     yield from compute_subscriptions(
         feedbin.states(),
-        feedly .states(),
+        feedly.states(),
     )