fix(actions): wait for transient hunk cache

Hunk-selecting actions can run while an async update has invalidated
the cached hunk list but has not repopulated it yet. In that state,
hunk selection treated the missing cache as an empty hunk list and
could skip the requested action.

Wait for the relevant unstaged or staged hunk cache before selecting a
hunk so those actions do not make decisions from transient cache state.

Assisted-by: Codex