Before 23.05, programs.swaylock.enable implicitly followed whether
programs.swaylock.settings was non-empty. That compatibility path was
still active for older state versions, but it emitted no warning.
Route the default through the shared state-version helper so legacy
users get the standard deprecation warning before the implicit enable
behavior is removed. Add a focused current-state-version test and keep
the existing legacy and explicit-enable coverage in place.
Signed-off-by: Austin Horstman <khaneliman12@gmail.com>
