feat: add source selectors and cooldown memo

src/polygateway/sources.py

@@ -0,0 +1,61 @@
+"""选源策略与源冷却备忘(M1 设计 §2.3;蓝本 CHS app/providers/selector.py 与 governance.py:107)。
+
+选源是端口(SourceSelector),两个首发实现逐字移植 CHS;冷却备忘是
+RetryMW 的进程本地状态——熔断开路的源在本地记冷却截止,选源时跳过,
+避免每轮白烧 RPM 去探测已知开路的源。
+"""
+
+from __future__ import annotations
+
+import time
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from collections.abc import Callable
+
+    from polygateway.types import SourceConfig, SourceStats
+
+
+class RoundRobinSelector:
+    """轮转起点后移(CHS selector.py:20 同款);单 client 内游标推进。"""
+
+    def __init__(self) -> None:
+        self._n = 0
+
+    def order(
+        self, sources: list[SourceConfig], stats: dict[str, SourceStats]
+    ) -> list[SourceConfig]:
+        if not sources:
+            return []
+        k = self._n % len(sources)
+        self._n += 1
+        return sources[k:] + sources[:k]
+
+
+class LeastInflightSelector:
+    """最少在途优先(CHS selector.py:36 同款);排序稳定,平局保持配置序。"""
+
+    def order(
+        self, sources: list[SourceConfig], stats: dict[str, SourceStats]
+    ) -> list[SourceConfig]:
+        return sorted(sources, key=lambda s: stats[s.name].inflight if s.name in stats else 0)
+
+
+class SourceCooldownMemo:
+    """进程本地的源冷却备忘(CHS governance.py:107 同款)。
+
+    只记"冷却截止时刻";set_until 取更晚者,防止较早的提示回退已有备忘。
+    """
+
+    def __init__(self, now: Callable[[], float] = time.monotonic) -> None:
+        self._now = now
+        self._until: dict[str, float] = {}
+
+    def set_until(self, source_name: str, until: float) -> None:
+        self._until[source_name] = max(self._until.get(source_name, 0.0), until)
+
+    def active(self, source_name: str) -> bool:
+        return self._until.get(source_name, 0.0) > self._now()
+
+    def remaining(self, source_name: str) -> float:
+        return max(0.0, self._until.get(source_name, 0.0) - self._now())