Refixes | Bug fixes & optimizations

Crash fixes

• Added a deadlock guard for section-load backoff, so a failed section load can't hang the world thread.
• Hardened the fluid pre-process injection for 0.6.4
• Restricted the collision fluid-section cache to FluidSection lookups and clear it on clear/setWorld.
• Skip despawn ticks for entities with null despawn components or timestamps.
• Prune invalid and foreign-store player refs from NPC interactable sets in StateSupport, replacing the old catch-and-discard wrapper.
• Retargeted entity-loader and related mixins to 0.6.4's section-based engine classes.
• Performance
• Pathfinding budget hooks retargeted to 0.6.4's ExecutionSupport-based steering signatures.
• New ScanShards option spreads throttler freeze admissions across scans.
• New options: StepWithoutPlayers, ThrottleExcludeAirborneOrDead andThrottleExcludeFlying which defaults to exempt.
• Hot radius now follows each world's own TPS with fraction-based bands.
• New opt-in heap-pressure guard lowers the server view radius under sustained post-GC pressure and restores it on recovery.
• TickSleep promoted from opt-in runtime flag to default-on helper, now hybrid spin + parkNanos wait.
• Split the coarse ParallelEntityTicking bundle into independent Parallel.* toggles. These are experimental and not recommended for production.

Content Handling

• Unknown-block cleaner gained opt-in scopes for fluids, container items, and player inventories.
• New SharedInstanceStorage backend for persistent shared instance worlds, behind the experimental SharedInstances patch.
• Chunk loader ported to use section storage

Maintenance

• Removed mixins made obsolete by the 0.6 section rework and related cleanups (ChunkSavingSystems, StatModifiersManager, RespawnBlockFixSystem, ActiveChunkUnloader, InstancePositionTracker, CraftingManagerAccessor).
• Prefab browser uses the engine's native filename recognition and suffix stripping instead of a hardcoded .prefab.json.