Merge branch 'main' into feat/plugin-feature

Resolve five conflicts, all of which needed both sides rather than a pick:

- BackgroundSlicingProcess: ours was a pure tabs->spaces reformat of base, so
  keep main's per-filament volume/nozzle map read-back (its only change here).
- GUI_App: main's #12506 else-if attached to an `if` this branch deleted;
  re-expressed onto the same-agent early-return path (the agent factory caches
  per id, so pointer equality is the same predicate).
- MainFrame: both sides relocated Sync Presets independently; keep main's
  push_notification plus the branch's Plugins menu items.
- Tab: the "TODO: Orca: Support hybrid" blocks were unchanged base, not a branch
  decision; take main's enabled Hybrid to match the already auto-merged siblings.
- test_config: union of both sides' cases (6 plugin + 9 multi-nozzle).

tests/libslic3r/CMakeLists.txt

@@ -12,6 +12,8 @@ add_executable(${_TEST_NAME}_tests
     test_clipper_offset.cpp
     test_clipper_utils.cpp
     test_config.cpp
+    test_config_variant_expansion.cpp
+    test_toolordering_nozzle_group.cpp
     test_preset_bundle_loading.cpp
     test_preset_setting_id.cpp
     test_preset_diff.cpp
@@ -21,9 +23,11 @@ add_executable(${_TEST_NAME}_tests
     test_polygon.cpp
     test_mutable_polygon.cpp
     test_mutable_priority_queue.cpp
+    test_nozzle_volume_type.cpp
     test_stl.cpp
     test_meshboolean.cpp
     test_marchingsquares.cpp
+    test_utils.cpp
     test_timeutils.cpp
     test_voronoi.cpp
     test_optimizers.cpp