* fix(ibus): require a real IM engine on Wayland (#478)
On Wayland a bare xkb:* IBus engine is a layout passthrough that never
delivers commit_text() to applications, so selecting the IBus backend
there silently no-ops (niri/sway, and GNOME/Mutter via the env-var
branch). Require a real IM engine before treating IBus as active on
Wayland, regardless of how it was detected; X11/XWayland (XIM) is
unchanged. Complements #486's compositor denylist.
* test(ibus): bind #478 patches to the module under test
Patch get_current_engine/is_ibus_daemon_running via patch.object on a
held ibus_engine reference and call is_ibus_active_input_method through
it, so the patched functions and the function under test always share
one module object. Fixes flakiness in the full CI suite where other test
files re-import ibus_engine and the dotted-string patch bound a
different module object.
