misc: fix all ty diagnostics

ty reported 20 diagnostics, and 0.0.89 adds a few more; this clears
them all without suppressions.

- The quest monster is held in a local before being stored on the
  quest book, so its name no longer reads from an Optional.
- PgUp/PgDn narrow the focused window with isinstance against a
  runtime-checkable PageScrollable protocol instead of hasattr.
- The ^t cheat used to monkeypatch SignalMixin.emit. SignalMixin now
  has a muted() context manager that emit() checks, and it restores
  emission even if a tick raises.
- GameView keeps its children as GameWindow, a protocol declaring
  stop() and sync(), so the cheat's resync type-checks.
- curses.ascii is imported explicitly where it is used.
- ProgressBarWindow is now Focusable itself, instead of calling
  Focusable.focus_standout() on a class that is not Focusable. Its
  four subclasses drop the duplicate Focusable base; the MRO and
  initialisation order are unchanged.
- MainMenu narrows the Optional pad before colouring the logo.
- The tests that record tasks assert player.task is set.
- Context managers are annotated as Generator rather than Iterator,
  which ty flags as deprecated for @contextmanager.
- The redundant cast() around getch() is gone.
- The frozen GameData test assigns through setattr(), since the
  direct assignment is an error by design.

Bug fixes:

- ListBox.select(None) crashed on `None < 0`; it now clears the
  selection, as DataTable.select(None) already does.
- ListBox.get() caught ValueError, which indexing never raises; it
  now catches IndexError, so an out-of-range index returns None as
  intended.

tests/test_game_data.py

@@ -179,4 +179,4 @@ def test_game_data_is_immutable() -> None:
     data = load_game_data()
     assert isinstance(data, GameData)
     with pytest.raises(AttributeError):
-        data.spells = ()  # type: ignore[misc]
+        setattr(data, "spells", ())