feat: add in-memory limiter and breaker satisfying backend contracts

tests/contracts/conftest.py

@@ -0,0 +1,61 @@
+"""契约测试共享 fixture: 后端参数化(M1 仅 memory,M2 增 redis 零改测试)。
+
+FakeClock 仅对支持时钟注入的后端有效(memory);M2 接入 Redis 后端时,
+依赖时钟推进的用例按后端能力跳过或改用真实等待。
+"""
+
+import pytest
+
+from polygateway.backends.memory.breaker import InMemoryGate
+from polygateway.backends.memory.limiter import InMemoryLimiter
+from polygateway.types import BreakerConfig, GlobalLimits, SourceConfig
+
+
+class FakeClock:
+    """确定性单调时钟;契约测试推进时间验证租约/冷却语义。"""
+
+    def __init__(self, start: float = 1000.0) -> None:
+        self.t = start
+
+    def __call__(self) -> float:
+        return self.t
+
+    def advance(self, seconds: float) -> None:
+        self.t += seconds
+
+
+def make_source(name: str = "s1", **overrides) -> SourceConfig:
+    base = dict(
+        name=name, provider="openai", base_url="https://gw.example/v1",
+        api_key="sk-test", model="m", timeout_s=10.0,
+    )
+    base.update(overrides)
+    return SourceConfig(**base)
+
+
+@pytest.fixture
+def clock() -> FakeClock:
+    return FakeClock()
+
+
+@pytest.fixture(params=["memory"])
+def limiter_factory(request, clock):
+    """返回 (sources, global_limits, lease_ttl_s) -> RateLimiter 的工厂。"""
+
+    def make(sources: list[SourceConfig], global_limits: GlobalLimits, lease_ttl_s: float = 100.0):
+        return InMemoryLimiter(
+            scope="llm", sources={s.name: s for s in sources},
+            global_limits=global_limits, lease_ttl_s=lease_ttl_s, now=clock,
+        )
+
+    return make
+
+
+@pytest.fixture(params=["memory"])
+def gate_factory(request, clock):
+    """返回 (BreakerConfig) -> ProviderGate 的工厂。"""
+
+    def make(config: BreakerConfig):
+        return InMemoryGate(config=config, now=clock)
+
+    return make