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).

src/libslic3r/CMakeLists.txt

@@ -221,6 +221,7 @@ set(lisbslic3r_sources
     GCode/FanMover.hpp
     GCode/GCodeProcessor.cpp
     GCode/GCodeProcessor.hpp
+    GCode/ElegooGCodeProcessorHelper.cpp
     GCode.hpp
     GCode/PchipInterpolatorHelper.cpp
     GCode/PchipInterpolatorHelper.hpp
@@ -468,6 +469,8 @@ set(lisbslic3r_sources
     FilamentGroup.cpp
     FilamentGroupUtils.hpp
     FilamentGroupUtils.cpp
+    MultiNozzleUtils.hpp
+    MultiNozzleUtils.cpp
     GCode/ToolOrderUtils.hpp
     GCode/ToolOrderUtils.cpp
     FlushVolPredictor.hpp