free the buffer setup and belt registration from BuildingSystem

Prerequisite for ConstructionSystem completing a building itself rather than
handing a finished site back: materialisation needs the buffer initialisers and
the BeltSystem registration, and both were BuildingSystem members.

initBuffers turned out to need nothing at all — it works purely on the Building
and RecipeDef it is given. The other three need only the config.
reregisterBeltTile takes BeltSystem and the config; it stays shared rather than
moving, because cancelDeconstruction and rotateInPlace use it too and are staying
on BuildingSystem.

Verified with a golden-checksum capture before and after — all four sample ticks
identical.

Co-Authored-By: Claude <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01YHcUerKAZKWNvSKJxYKbnG

src/lib/sim/BuildingBuffers.h

@@ -0,0 +1,39 @@
+#pragma once
+
+#include <vector>
+
+#include "BeltSystem.h"
+#include "Building.h"
+#include "GameConfig.h"
+#include "ItemType.h"
+#include "RecipesConfig.h"
+
+// Setting a building up when it starts existing or is reconfigured: sizing its
+// input/output buffers from what it will produce, and handing belt-like types back
+// to BeltSystem. Free functions over the config and the building — they read no
+// factory state, so both BuildingSystem and ConstructionSystem can use them.
+
+// Buffers for a building running one known recipe: inputs capped at twice each
+// ingredient's per-cycle amount, output at twice the per-cycle total (one cycle's
+// max for a Reprocessing Plant, REQ-MAT-OUTPUT-BUFFER-REPROCESSING).
+void initBuffers(Building& b, const RecipeDef& recipe);
+
+// Buffers for an auto-recipe building (Smelter, Reprocessing Plant), unioned over
+// every recipe of its type (REQ-BLD-SMELTER, REQ-BLD-REPROCESSING).
+void initAutoBuffers(const GameConfig& config, Building& b);
+
+// Buffers for a shipyard: its schematic's materials plus those of every placed
+// module (REQ-BLD-SHIPYARD).
+void initShipyardBuffers(const GameConfig& config, Building& b);
+
+// The Salvage Bay holds no recipe inputs; its output capacity is config-defined
+// (REQ-BLD-SALVAGE-BAY).
+void initSalvageBayBuffer(const GameConfig& config, Building& b);
+
+// Registers a belt, splitter or tunnel end with BeltSystem. A splitter's filters
+// live in BeltSystem and are lost by removeTile, so they are passed back in
+// (REQ-BLD-SPLITTER). No-op for every other building type.
+void reregisterBeltTile(BeltSystem& belts, const GameConfig& config,
+                        const Building& building,
+                        const std::vector<ItemType>& splitterFilterA,
+                        const std::vector<ItemType>& splitterFilterB);