Add binary scenery format (eu7 v3) with async baking, replacing SBT

Text scenery component files (.scn/.inc/.scm/.ctr) are compiled into
per-file binary twins (.scnb/.incb/.scmb/.ctrb), handled transparently
at the cParser layer: a fresh twin (mtime-checked, version-matched) is
replayed instead of re-tokenizing text; otherwise the text is parsed and
a twin is compiled alongside it for next time.

Format details:
- per-file string interning: keywords/paths stored once, referenced by
  varint index (so node/endmodel/... are not repeated as text)
- numeric tokens stored as 8-byte IEEE doubles, not ASCII
- includes kept as references with parameters; random sets stored verbatim
  and re-evaluated on every load (choice not frozen at compile time)
- twin writing offloaded to a bounded thread pool so baking overlaps
  scene construction instead of blocking the load

The legacy terrain-only .sbt path is removed; terrain now loads as
ordinary scenery content.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

utilities/Globals.cpp

@@ -632,9 +632,9 @@ bool global_settings::ConfigParseSimulation(cParser& Parser, const std::string&
         return true;
     }
 
-    if (token == "file.binary.terrain")
+    if (token == "file.binary.scenery")
     {
-        ParseOne(Parser, file_binary_terrain, 1, false);
+        ParseOne(Parser, file_binary_scenery, 1, false);
         return true;
     }
 
@@ -1587,7 +1587,7 @@ global_settings::export_as_text( std::ostream &Output ) const {
     export_as_text( Output, "multisampling", iMultisampling );
     export_as_text( Output, "latitude", fLatitudeDeg );
     export_as_text( Output, "convertmodels", iConvertModels );
-    export_as_text( Output, "file.binary.terrain", file_binary_terrain );
+    export_as_text( Output, "file.binary.scenery", file_binary_scenery );
     export_as_text( Output, "inactivepause", bInactivePause );
     export_as_text( Output, "slowmotion", iSlowMotionMask );
     export_as_text( Output, "hideconsole", bHideConsole );