feat(circuit-breaker): read-only state introspection (0.14.0)

[lesnik512]

Summary

Exposes the circuit breaker's current state read-only, via a public CircuitState enum and a state property on both AsyncCircuitBreaker and CircuitBreaker — for health/readiness endpoints, dashboards, and tests.

from httpware import CircuitState
from httpware.middleware.resilience import AsyncCircuitBreaker

breaker = AsyncCircuitBreaker(failure_threshold=5)
# ... in a readiness handler:
if breaker.state is CircuitState.OPEN:
    ...  # report the dependency as degraded

Closes the cheap half of the deferred CircuitBreaker introspection item (manual control force_open/force_closed stays deferred). Ships as 0.14.0 (additive, no breaking changes).

What's in it

• Public CircuitState enum — promoted from the private _CircuitState (CLOSED/OPEN/HALF_OPEN); exported from httpware and httpware.middleware.resilience.
• state property on both wrappers — a pure read of the stored state: no lock, no clock, and it never triggers the lazy OPEN→HALF_OPEN transition (that stays in admit, on the next request after reset_timeout). So state reports OPEN until a request is actually admitted as the probe — documented as the raw-read caveat.
• Docs — architecture/resilience.md, docs/resilience.md, and 0.14.0 release notes.

No behavior change to either trip mode; version is tag-driven, so pyproject.toml is untouched.

Design + plan: planning/changes/active/2026-06-16.03-circuit-breaker-state/.

Test plan

• just test — 704 passed, 100% coverage
• just lint — clean (ruff format/check + ty)
• State tests (async + sync): CLOSED → OPEN → HALF_OPEN → CLOSED lifecycle; raw-read caveat (stays OPEN past reset_timeout with no request); public-API export + identity
• Classic + rate-mode behavior unchanged
• mkdocs build --strict — clean

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