Add a per-origin circuit breaker to ofetch

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What this task asks for

Add an opt-in per-origin circuit breaker for fetch requests with half-open probing and shared state across clients. Add an opt-in per-origin circuit breaker with documented defaults for threshold, cooldown, probes, and failure statuses. Transition deterministically between closed, open, and half-open states using `Date.now()`. Resolve state keys from the effective request origin and share state across clients derived from one parent. Limit concurrent half-open probes and keep each probe slot for the full logical request including retries. Count each failed logical request once across network, body, parsing, hook, and configured status failures. Reject open or over-quota requests before fetch with an error containing `Circuit breaker is open`.