Add EU7 PACK v11 UTEX, section unload, and LRU streaming caches

Bake deduplicated section texture lists (UTEX) and read them at runtime so
texture warm/prefetch no longer scans every instance. Evict PACK sections
outside a 16 km keep ring and cap mesh/nodedata/texture warm caches to stop
RAM and apply cost from growing without bound during long fast camera flight.

- Bake v11 (format=4): UMES + UTEX + CHNK; mesh/texture ordering by frequency
- Runtime: incremental UTEX warm, adaptive apply slices, preempt/catchup tuning
- Unload: track instances per section, Region erase, pack pool release
- LRU: mesh/nodedata (2000, ref-counted), warmed textures (2048)
- Bench/diagnostics: unload and cache eviction counters
- Fix pack instance erase in Region; resolve duplicate helper symbols

scene/eu7/eu7_model_prefetch.h

@@ -13,9 +13,12 @@ http://mozilla.org/MPL/2.0/.
 
 #include <cstddef>
 #include <string>
+#include <unordered_map>
 #include <unordered_set>
 #include <vector>
 
+class TModel3d;
+
 namespace scene::eu7 {
 
 // Tylko warm_instanceable_cache dla juz zcache'owanych meshy (bez cold GetModel na workerze).
@@ -30,10 +33,23 @@ preload_pack_models(
 
 // Main thread: Fetch_Material dla unikalnych texture_file z chunka przed apply.
 // Zwraca liczbe unikalnych Fetch_Material w tym slice.
+std::size_t
+warm_pack_texture_paths_main(
+    std::string const *paths,
+    std::size_t count,
+    double budget_ms = 0.0,
+    std::size_t *processed_out = nullptr );
+
 std::size_t
 warm_pack_textures_main( Eu7Model const *models, std::size_t count );
 
 void
 reset_pack_texture_warm_cache();
 
+// Thread-safe cold mesh load: session cache, then GetModel under g_pack_mesh_load_mutex.
+[[nodiscard]] bool
+ensure_pack_mesh_in_session_cache(
+    std::string model_file,
+    std::unordered_map<std::string, TModel3d *> &session_cache );
+
 } // namespace scene::eu7