fix: close db watch change iterator on exit

[immanuwell]

A canceled db/watch leaves its deletion tracker registered.
That can keep deleted objects in the graveyard until runtime cleanup kicks in

This closes the change iterator when the command exits.
The test runs the real script command and checks the tracker returns to zero

Repro:

1. Run the new test against main
2. It fails because the tracker stays at 1
3. Apply the fix, it returns to 0

Tested with make