Add EU7 PACK v12 PROT/INST and tune streaming apply path

Introduce EU7B v8 bake with global PROT chunk and v12 section payloads
(solo MODL + compact inst records, per-chunk solo/inst tables). Reader
parses v12 with chunked decode and v11→flat fallback; fix chunk blob
layout to write solo blocks before inst records.

Streaming: add unload keep-radius hysteresis on deceleration, ring-deficit
urgent drain, higher cold-mesh/apply budgets, and smarter warm-prefix
preload. Move UMES mesh prefetch to the main thread and route PACK apply
through ensure_pack_mesh_in_session_cache to avoid GetModel races on
Global.asCurrentTexturePath; harden MdlMngr texture-path trimming.

Rebake root scenario .eu7 files to get v12; existing v7–v11 packs remain
readable.

scene/eu7/eu7_pack_bench.cpp

@@ -186,6 +186,9 @@ log_pack_bench_impl( Eu7PackBench const &bench, char const *const title ) {
         " cam=" + std::to_string( bench.stream_dequeue_camera ) +
         " wait_near=" + std::to_string( bench.stream_dequeue_wait_near ) +
         " block_far=" + std::to_string( bench.stream_jobs_blocked_far ) +
+        " block_ring_in=" + std::to_string( bench.stream_jobs_blocked_ring_inner ) +
+        " block_ring_out=" + std::to_string( bench.stream_jobs_blocked_ring_outer ) +
+        " defer_dist=" + std::to_string( bench.stream_worker_deferred_distant ) +
         " stuck_skip=" + std::to_string( bench.stream_apply_stuck_skip ) );
     WriteLog(
         "  diag ready_tex_ms=" + std::to_string( static_cast<int>( bench.stream_prefetch_ready_tex_ms ) ) +