feat(engine): wire the per-filament volume-map producer pipeline

- Print::update_filament_maps_to_config takes filament/volume/nozzle
  maps, backfills an empty volume map from extruder types, rebuilds
  filament_map_2, re-expands the per-filament variant arrays, and
  recomputes retract overrides keyed by resolved slots
- grouping writes its result back in every non-sequential mode;
  manual multi-nozzle grouping validates the user mapping and raises a
  translatable error on deviation; the engine's concrete volume
  assignment is deliberately not merged yet (per-filament arrays are
  already consumed by filament id, so materializing High Flow now
  would change motion before the layer-aware resolvers land)
- Print::apply treats the three map keys as engine outputs in auto
  modes (erased from the diff and adopted), compares them against used
  filaments in manual mode, and keeps the pre-expansion snapshot in
  sync with the late normalization pass so rebuilt headers reflect the
  sliced state instead of resurrecting stale values
- volume/nozzle maps and extruder_nozzle_stats join the invalidation
  group of filament_map (wipe tower + skirt/brim)
- PresetBundle composes full configs with an optional per-filament
  volume map (plate map, else defaults derived from each extruder's
  flow type); project config keeps the map sized across filament
  count changes
- PartPlate stores per-plate volume/nozzle maps; Plater injects them
  at every slice-composition site (incl. g-code reload and wipe-tower
  estimation); BackgroundSlicingProcess reads engine results back to
  the plate in auto modes
- per-filament map trust guards relaxed to size-match everywhere now
  that every producer sizes the map; single-filament explicit flow
  assignments are honored
- tests: grouping volume maps stay concrete, merge semantics of
  update_used_filament_values, single-filament override honoring

Motion g-code is byte-identical fleet-wide including Hybrid projects
(19-fixture gate + repro determinism double-slice). Header deltas:
the map keys now dump real values, and stale pre-normalization values
(e.g. enable_prime_tower on single-used-filament prints) no longer
leak into the config block.

tests/libslic3r/test_config_variant_expansion.cpp

@@ -288,14 +288,15 @@ TEST_CASE("update_values_to_printer_extruders_for_multiple_filaments resolves pe
         REQUIRE(config.option<ConfigOptionInts>("filament_self_index")->values == std::vector<int>({1, 2}));
     }
 
-    SECTION("a single-filament map matches the registered default's shape and is ignored") {
+    SECTION("a single-filament explicit assignment on a Hybrid extruder is honored") {
         DynamicPrintConfig config = make_hybrid_printer_config();
         config.option<ConfigOptionInts>("filament_self_index", true)->values = {1, 1};
         config.option<ConfigOptionStrings>("filament_extruder_variant", true)->values = {"Direct Drive Standard", "Direct Drive High Flow"};
         config.option<ConfigOptionFloats>("filament_max_volumetric_speed", true)->values = {12., 20.};
         config.option<ConfigOptionInts>("filament_map", true)->values = {2};
-        // sized to the (single) filament count, but indistinguishable from the registered
-        // 1-element default, so it must not override slot resolution
+        // sized to the (single) filament count: the producers guarantee sizing, so a
+        // single-filament map is as trustworthy as any other and the explicit High Flow
+        // request must win over the Hybrid->Standard fallback
         config.option<ConfigOptionInts>("filament_volume_map", true)->values = {nvtHighFlow};
 
         std::vector<std::vector<NozzleVolumeType>> nozzle_volume_types;
@@ -305,8 +306,7 @@ TEST_CASE("update_values_to_printer_extruders_for_multiple_filaments resolves pe
         config.update_values_to_printer_extruders_for_multiple_filaments(config, extruder_count, count, filament_keys,
             "filament_self_index", "filament_extruder_variant");
 
-        // Hybrid resolves as Standard, exactly as if no map were present
-        REQUIRE(config.option<ConfigOptionFloats>("filament_max_volumetric_speed")->values == std::vector<double>({12.}));
+        REQUIRE(config.option<ConfigOptionFloats>("filament_max_volumetric_speed")->values == std::vector<double>({20.}));
         REQUIRE(config.option<ConfigOptionInts>("filament_self_index")->values == std::vector<int>({1}));
     }