…tion

`finalize_item_locations()` does not mutate `self` or any attribute of
`self`, so fill_slot_data does not need to wait for
`finalize_item_locations()` to be run.

Previously, before 113c54f, synchronization was necessary because
`finalize_item_locations()` would set location data into
`self.zz_system.patcher`, which `fill_slot_data` would then read from.

This also means that Zillion can be re-enabled for the
test.general.test_implemented.test_slot_data test.

This reverts commit 73f30de.

…chronization"

This reverts commit e18906b.

…ot_data

`generate_output` and `fill_slot_data` are run in separate threads so
there is no guarantee that one runs before the other.

Before this patch, the threads were synchronized by making
`fill_slot_data` wait for `generate_output`. The problem with doing this
is that the test.general.test_implemented.test_slot_data test does not
run `generate_output`, so Zillion had to be disabled from the test.

This patch changes the synchronization of the threads such that it does
not matter which function is run first. Whichever function is run first
will run `finalize_item_locations()` and the other function will wait
until `finalize_item_locations()` is complete and has been cached in a
new instance attribute.

Zillion has now been re-enabled for the
test.general.test_implemented.test_slot_data test.