refactor(auto-router compression): resolve the policy without a loop-local rebind

The marker walk rebound a loop-local on each iteration, which is the mutation the
repository's convention exists to discourage, but a `: Final` cannot express that
inside a loop body: basedpyright rejects it outright with 'A Final variable cannot
be assigned within a loop'. A lazy generator binds the name once per item and never
rebinds it, so the first marker carrying a policy still wins and the rest are never
read.

litellm/proxy/guardrails/auto_router_compression.py

@@ -117,11 +117,11 @@ def policy_for_model(
     # request does not carry describes a different slice of traffic, so falling back
     # to it would apply, say, an "eu" policy to a "us" request purely on config order.
     untagged: Final = tuple(params for params in markers if not params.get("tags"))
-    for params in (*tag_matched, *untagged):
-        policy = policy_from_litellm_params(params)
-        if policy is not None:
-            return policy
-    return None
+    # Lazily, so the first marker carrying a policy still wins and the rest are never
+    # read. A generator rather than a loop-local: the name is bound once per item and
+    # never rebound, which `: Final` cannot express inside a loop body.
+    candidates: Final = (policy_from_litellm_params(params) for params in (*tag_matched, *untagged))
+    return next((policy for policy in candidates if policy is not None), None)
 
 
 def team_id_from_request(request_kwargs: Mapping[str, object]) -> str | None: