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_pack_bench.h

@@ -72,7 +72,14 @@ struct Eu7PackBench {
     std::uint64_t stream_dequeue_wait_near { 0 };
     std::uint64_t stream_jobs_blocked_far { 0 };
     std::uint64_t stream_apply_stuck_skip { 0 };
+    std::uint64_t stream_sections_unloaded { 0 };
+    std::uint64_t stream_unload_instances { 0 };
+    std::uint64_t stream_mesh_cache_evictions { 0 };
+    std::uint64_t stream_nodedata_cache_evictions { 0 };
+    std::uint64_t stream_texture_cache_evictions { 0 };
     double stream_prefetch_ready_tex_ms { 0.0 };
+    double stream_prefetch_ready_umes_ms { 0.0 };
+    std::uint64_t stream_prefetch_ready_umes_loads { 0 };
     std::uint64_t peak_pending_total { 0 };
     std::uint64_t stream_inst_planned { 0 };
     std::uint64_t stream_inst_after_cold { 0 };
@@ -92,6 +99,7 @@ struct Eu7PackBench {
     std::uint64_t peak_chunk_instances { 0 };
     std::uint64_t peak_chunk_cold { 0 };
     double last_chunk_ms { 0.0 };
+    double last_apply_ms { 0.0 };
     std::uint64_t last_chunk_instances { 0 };
     std::uint64_t last_chunk_cold { 0 };