Follow-up to #14785. Routes the tests that still hand-rolled temp paths through
the shared helpers and unifies the temp guards.
- Add ScopedTemporaryDir and a shared ScopedTemporaryPath base under it and
ScopedTemporaryFile.
- Move test_3mf's round-trip .3mf output out of the TEST_DATA_DIR source tree
(a fixed-name leak) and test_toolordering's fixed-name temp .gcode (a sharding
collision) onto ScopedTemporaryFile.
- Move test_config, test_slicing_pipeline_bindings, the test_3mf backup dirs, and
test_preset_bundle_loading onto the guards.
- Make slic3rutils ScopedDataDir compose ScopedTemporaryDir; dedupe
test_network_versions' fixture and delete test_plugin_lifecycle's duplicate.
* fix: impl refactor
* fix: unload/load python module, race conditions, freezes
* remove dead code
* remove extra hook
* remove more dead code
* fix gil run script
