A respawn into another level of the same dimension type makes a new level

ClientPacketListener.handleRespawn keeps its ClientLevel only when the
spawn's level key is the current level's, and makes a new one otherwise.
Horizon compared the dimension type's name, so moving between two levels
sharing a type (a data pack or mod dimension using the Overworld's) kept the
old level's chunks and entities, and fired neither native_client_level_load
nor native_client_level_unload. It now compares the level key the client
last entered (heard_level), so such a move clears the world and fires both
hooks, with the right level named on the next unload.

Fixes #6316

Co-Authored-By: Claude Opus 5.5 <[email protected]>

crates/horizon-client/src/game/remote.rs

@@ -1997,7 +1997,9 @@ impl Game<'_> {
             dimension.has_skylight,
         )
         .unwrap_or_else(|_| super::Dim::from_id(&dimension.name).shape());
-        let same = r.dimension.name == dimension.name && keep_world;
+        // handleRespawn keeps the ClientLevel only for the same level key:
+        // two levels sharing a dimension type are still two levels.
+        let same = keep_world && r.heard_level.as_deref() == Some(spawn.dimension.as_str());
         r.chunk_format = Arc::new(
             r.chunk_format
                 .with_dimension(&dimension)