relationship requires a more performant and powerful way to manage query's state, as archetype fragmentation becomes prevalent when relationships are used.

This goal can be achieved through 'Query as Entities' – a pattern that selectively exposes new/deleted archetypes only to affected queries requiring iteration over them.

There are some excellent PRs that have tried to implement it for Bevy: #14668 , #18860

Implementation Steps:

• Trigger an event when a new archetype is created.
• Componentize system-internal QueryState.
• Use Observer to manage query entities.
• Type-erased QueryState Component.
• (optional) Provide users with a more ergonomic way to use managed QueryState.
• (optional) To optimize, only notify observers of impacted query entities instead of iterating over every query entity.