extract the production rules as free functions over config and building

src/lib/sim/BuildingSystem.h

@@ -16,6 +16,7 @@
 #include "BeltSystem.h"
 #include "Building.h"
 #include "FactoryState.h"
+#include "ProductionRules.h"
 #include "BuildingType.h"
 #include "BuildingId.h"
 #include "GameConfig.h"
@@ -27,18 +28,6 @@
 
 class Hasher;
 
-// Production state of a building for the UI status light (REQ-UI-STATUS-LIGHT).
-// The simulation owns the classification so it stays in sync with the
-// production-cycle predicates (REQ-MAT-CYCLE); the UI maps each value to a fill
-// color.
-enum class ProductionStatus
-{
-    Unconfigured,  // no recipe/schematic selected (grey)
-    Producing,     // a production cycle is active (green)
-    Starved,       // idle: a required input is missing / Salvage Bay empty (red)
-    Blocked,       // idle: output buffer full, inputs otherwise present (yellow)
-};
-
 // Manages building placement, construction queuing, and the per-tick
 // production loop (belt→building pull, production, building→belt push).
 // All types including Belt and Splitter are stored as Building instances;
@@ -150,7 +139,6 @@ public:
     // nullopt for building types that show no light (belts, splitters, tunnels,
     // HQ, defence stations). The Salvage Bay is a two-state special case:
     // Producing while its output buffer holds scrap, Starved when empty.
-    std::optional<ProductionStatus> getProductionStatus(const Building& building) const;
     std::vector<BeltTileInfo> getAllBeltTiles()             const;
 
     // Visits every item currently emerging from a building output port on its
@@ -245,17 +233,12 @@ private:
     // building (Smelter, Reprocessing Plant) offers every recipe of its type with
     // inputs; other buildings offer only their selected recipe. Shared by
     // tickProduction and the status classifier (REQ-MAT-CYCLE, REQ-UI-STATUS-LIGHT).
-    std::vector<const RecipeDef*> gatherCandidateRecipes(const Building& b) const;
     // True if every input of `recipe` is present in `b`'s input buffers in the
     // required per-cycle amount (REQ-MAT-CYCLE input check).
-    bool                recipeInputsAvailable(const Building& b,
-                                              const RecipeDef& recipe) const;
     // Combined base + module materials a shipyard needs per ship (REQ-BLD-SHIPYARD).
-    std::map<std::string, int> computeShipyardRequiredMaterials(const Building& b) const;
     // True if the building currently has all inputs/materials to start a cycle
     // (ignoring output-buffer space); drives the Starved/Blocked distinction of
     // the status light (REQ-UI-STATUS-LIGHT).
-    bool                hasInputsToStart(const Building& b) const;
 
     void                initBuffers(Building& b, const RecipeDef& recipe) const;
     // Buffers for an auto-recipe building (Smelter, Reprocessing Plant): input