Fix chunk unloading regression from upstream merge

Commit a24318ee changed drop() to immediately remove chunks from cache,
bypassing the deferred m_toDrop save/unload pipeline. This caused missing
chunks on dedicated servers, iterator invalidation in dropAll() and
ServerLevel::save(), and entity duplication (item frames) from chunks
being reloaded without their entities first being removed from the level.

- ServerChunkCache::drop(): restore m_toDrop queue instead of immediate
  cache removal, so tick() can save/unload/move to unloadedCache safely
- MultiPlayerChunkCache::drop(): restore soft-unload (keep chunk in cache
  with loaded=true) instead of nulling cache and hasData
- PlayerChunkMap::setRadius(): remove dropAll() call when reducing radius,
  the per-chunk removal loop already handles out-of-range chunks

Minecraft.Client/ServerChunkCache.cpp

@@ -91,11 +91,7 @@ void ServerChunkCache::drop(const int x, const int z)
 
 	if (chunk != nullptr)
 	{
-		const auto it = std::find(m_loadedChunkList.begin(), m_loadedChunkList.end(), chunk);
-		if (it != m_loadedChunkList.end()) m_loadedChunkList.erase(it);
-
-		cache[idx] = nullptr;
-		chunk->loaded = false;
+		m_toDrop.push_back(chunk);
 	}
 }