Allow queries to work without mutable world access #84
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Objective
Bevy is considering not allowing mutable world access in
WorldQuery::init_state.See here.
This PR explores how this crate might migrate if those changes go through.
Solution
Don't initialize the registry resource in
init_state.Use atomics to seal the registry.
There is one caveat.
Before this pr, if a component was registered for a trait after the query was made, it would panic.
After this pr, that panic will only happen if, when the query was made, there were already components registered for that trait.
Since both the warning and panic serve the same purpose (to remind users to actually register their components), I don't think this is a concern, but I wanted to be transparent about it.