LockedListProxy and LockedDictProxy subclass `list` and `dict` but
initialize the parent as empty (`super().__init__()`), delegating all
access to an internal `self._list` / `self._dict`. However, several
inherited methods were not overridden, causing them to silently operate
on the empty parent instead of the real data.
Most critically, `list.index()` always raises `ValueError` because it
searches the empty parent list. Other broken methods include `count()`
(always returns 0), `sort()`/`reverse()` (no-ops), `copy()` (returns
empty), and arithmetic operators (`+`, `*`).
All mutating operations acquire the lock; read-only operations delegate
directly to the underlying collection, consistent with existing pattern.
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