feat(gui): per-filament nozzle volume selection and persistence

- FilamentMapDialog's manual page understands volume types: a mixed
  (Hybrid) extruder shows separate Standard / High Flow drop zones
  with live sub-nozzle counts, a validation timer with an inline
  error + "set nozzle count" suggestion, and composes a per-filament
  volume map on OK (persisted to the plate or globally)
- switching an extruder's Flow type rewrites the affected plate map
  entries; plate maps stay sized across filament add/delete/count
  changes (values keep their filament, no index shift)
- CLI: manual mapping on multi-nozzle printers synthesizes the volume
  map from extruder flow types when absent; nozzle-manual mode
  requires explicit maps; computed maps land on the plate so exported
  projects carry filament_volume_maps
- filament_nozzle_map joins the project options (selection seeding +
  filament-count resizing)
- pot entries for the new dialog strings

All 19 reference fixtures byte-identical; slicing an exported Hybrid
project reproduces its g-code byte-for-byte with the volume map
round-tripped through model_settings.config.

src/slic3r/GUI/Widgets/MultiNozzleSync.cpp

@@ -35,7 +35,7 @@ static const int RightExtruderIdx = 1;
 // config key (ConfigOptionStrings, one encoded map per extruder) via get_extruder_nozzle_stats /
 // save_extruder_nozzle_stats_to_string. These helpers read and write that config.
 
-static int extruder_nozzle_count(PresetBundle *preset_bundle, int extruder_id, NozzleVolumeType volume_type)
+int getExtruderNozzleCount(PresetBundle *preset_bundle, int extruder_id, NozzleVolumeType volume_type)
 {
     if (!preset_bundle)
         return 0;
@@ -49,7 +49,7 @@ static int extruder_nozzle_count(PresetBundle *preset_bundle, int extruder_id, N
     return it == stats[extruder_id].end() ? 0 : it->second;
 }
 
-static int extruder_nozzle_count_total(PresetBundle *preset_bundle, int extruder_id)
+int getExtruderNozzleCountTotal(PresetBundle *preset_bundle, int extruder_id)
 {
     if (!preset_bundle)
         return 0;
@@ -230,8 +230,8 @@ void updateNozzleCountDisplay(PresetBundle *preset_bundle, int extruder_id, Nozz
 
     int display_count = -1; // hides the badge
     if (support_multi_nozzle)
-        display_count = volume_type == nvtHybrid ? extruder_nozzle_count_total(preset_bundle, extruder_id)
-                                                 : extruder_nozzle_count(preset_bundle, extruder_id, volume_type);
+        display_count = volume_type == nvtHybrid ? getExtruderNozzleCountTotal(preset_bundle, extruder_id)
+                                                 : getExtruderNozzleCount(preset_bundle, extruder_id, volume_type);
     plater->sidebar().set_extruder_nozzle_count(extruder_id, display_count);
 }
 
@@ -269,7 +269,7 @@ void onNozzleVolumeTypeSwitch(PresetBundle *preset_bundle, int extruder_id, Nozz
     // Hybrid is a mix, not a type every nozzle shares, so there is nothing to carry over.
     if (type == nvtHybrid)
         return;
-    const int total = extruder_nozzle_count_total(preset_bundle, extruder_id);
+    const int total = getExtruderNozzleCountTotal(preset_bundle, extruder_id);
     setExtruderNozzleCount(preset_bundle, extruder_id, type, total, true);
 }
 
@@ -294,14 +294,14 @@ void manuallySetNozzleCount(int extruder_id)
         return;
 
     const NozzleVolumeType volume_type    = NozzleVolumeType(nozzle_volume_type_opt->values[extruder_id]);
-    const int              standard_count = extruder_nozzle_count(preset_bundle, extruder_id, nvtStandard);
-    const int              highflow_count = extruder_nozzle_count(preset_bundle, extruder_id, nvtHighFlow);
+    const int              standard_count = getExtruderNozzleCount(preset_bundle, extruder_id, nvtStandard);
+    const int              highflow_count = getExtruderNozzleCount(preset_bundle, extruder_id, nvtHighFlow);
 
     // Require at least one nozzle for a Hybrid extruder (an empty mix is meaningless) and when the other
     // extruder currently has none.
     bool force_no_zero = volume_type == nvtHybrid;
     if (nozzle_volume_type_opt->values.size() > 1)
-        force_no_zero |= extruder_nozzle_count_total(preset_bundle, 1 - extruder_id) == 0;
+        force_no_zero |= getExtruderNozzleCountTotal(preset_bundle, 1 - extruder_id) == 0;
 
     ManualNozzleCountDialog dialog(wxGetApp().plater(), volume_type, standard_count, highflow_count, max_nozzle_count->values[extruder_id], force_no_zero);
     if (dialog.ShowModal() == wxID_OK) {

src/slic3r/GUI/Widgets/MultiNozzleSync.hpp

@@ -219,6 +219,11 @@ std::optional<NozzleOption> tryPopUpMultiNozzleDialog(MachineObject* obj);
 // counts are reset first.
 void setExtruderNozzleCount(PresetBundle *preset_bundle, int extruder_id, NozzleVolumeType type, int nozzle_count, bool clear_all);
 
+// Read one extruder's nozzle count for a volume type (or its total) from the edited printer preset's
+// `extruder_nozzle_stats` config key. Returns 0 when the stats are absent or the extruder is unknown.
+int getExtruderNozzleCount(PresetBundle *preset_bundle, int extruder_id, NozzleVolumeType volume_type);
+int getExtruderNozzleCountTotal(PresetBundle *preset_bundle, int extruder_id);
+
 // Refresh the sidebar nozzle-count badge for one extruder: shows the extruder's physical nozzle count on
 // multi-nozzle printers, hides it (count -1) everywhere else.
 void updateNozzleCountDisplay(PresetBundle *preset_bundle, int extruder_id, NozzleVolumeType volume_type);