fix(level): find a scene file's chunks and sections as the client does

SceneLoader::ReadLvlFile (1.10.64):
- chunked files: the file info chunk starts the file and gives where
  the environment, object and particle chunks start, 0 for none
  (DoLvlChunk, ReadLvlChunk1000); the reader walked the chunks one after
  another by their sizes instead;
- older files: the editor settings are a u32 size and that many bytes
  (SceneLoader::ReadEditorSettings, skipped by size); the reader took
  them for a u32 and then a count of 12 byte points;
- older files before version 3 have no objects for the client ("Level
  file is unsupported").

LevelFile now does the same. Every scene file on disk reads the same
objects as before.

Check in game: every world spawns its objects as before.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/dWebTests/LevelObjectsTests.cpp

@@ -32,6 +32,7 @@ namespace {
 		w.Put<uint32_t>(41).Put<uint32_t>(1).Put<uint32_t>(0).Put<uint32_t>(0).Put<uint32_t>(0);
 		w.End(info);
 		auto objects = w.Chunk(2001);
+		w.At<uint32_t>(info + 32, static_cast<uint32_t>(objects)); // the file info chunk says where the objects start, as in real files
 		w.Put<uint32_t>(4);
 		w.Object(4945, 10, 20, 30, "respawnname=0:NS_LW_Portal\ncustom_config_names=0:");
 		w.Object(6010, 1, 1, 1, "spawntemplate=1:6010");                                   // not a spawn point