Update the vision every time we step the game

Recalculate the character's lines of sight every time we step the game,
rather than just every time the character *moves*. I had originally
thought this was a non-contiguous lines-of-sight bug - which there's a
test disproving - but it actually turned out to be that actions like
eating or attacking would step the game forward (thus moving gormlaks)
without re-calculating the positions visible to the character.

src/Xanthous/App.hs

@@ -102,6 +102,8 @@ stepGameBy ticks = do
     pEntity' <- step ticks pEntity
     entities . ix eid .= pEntity'
 
+  modify updateCharacterVision
+
   whenM (uses character isDead)
     . prompt_ @'Continue ["dead"] Uncancellable
     . const . lift . liftIO
@@ -137,7 +139,6 @@ handleCommand (Move dir) = do
       characterPosition .= newPos
       stepGameBy =<< uses (character . speed) (|*| 1)
       describeEntitiesAt newPos
-      modify updateCharacterVision
     Just Combat -> attackAt newPos
     Just Stop -> pure ()
   continue