#### Brief overview of PR changes/additions
- A saved variable with a function, userdata or coroutine anywhere
inside it now exports only the members registered in `savedVars`, which
for a table ticked while empty is an empty group. Tables holding nothing
but data keep the full save added in #9762.
- The save-time walk records which saved globals hold such a value;
`XMLexport` turns the ride-along off for those variables only. Silent,
and it costs nothing outside a save.
- New `SavedVariableFenceTest` pins all 11 measured shapes, on disk and
after a reload.
#### Motivation for adding to Mudlet
A half-restored table defeats the `if next(t) == nil then rebuild() end`
guard packages carry, which kills cron-daemon's scheduler permanently on
its first minute wake after a restart.
#### Other info (issues closed, discussion etc)
Fixes#9857
**Test case:** install cron-daemon, tick `cron` in the Variables view,
add a job with a `command` function, restart and wait for the minute
rollover - the daemon keeps running (measured 2/2 canary fires, against
0/2 before).
Assisted-by: Claude:claude-opus-5
Signed-off-by: Vadim Peretokin <vadim.peretokin@mudlet.org>
