Async Resources in Reactor

Reactor replaces the UseState + UseEffect + manual-cancellation dance with three hooks. Reads return AsyncValue<T>, writes return a Mutation handle. The hook owns the cancellation token, dedups across siblings, caches results in a shared QueryCache, and drops late results on unmount.

Available on any Component subclass directly; on RenderContext as extension methods for function components (Memo(ctx => ...) or RenderEachTime(ctx => ...)).

1. UseResource — single fetch

AsyncValue<T> UseResource<T>(
    Func<CancellationToken, Task<T>> fetcher,
    object[] deps,
    ResourceOptions? options = null);