chore: ruff auto-fix PLR6201 — tuple → set in membership tests (#23937)

Replace  with  for all literal-tuple
membership tests. Set lookup is O(1) vs O(n) for tuple — consistent
micro-optimization across the codebase.

608 instances fixed via `ruff --fix --unsafe-fixes`, 0 remaining.
133 files, +626/-626 (net zero).

agent/credential_pool.py

@@ -149,7 +149,7 @@ class PooledCredential:
         }
         result: Dict[str, Any] = {}
         for field_def in fields(self):
-            if field_def.name in ("provider", "extra"):
+            if field_def.name in {"provider", "extra"}:
                 continue
             value = getattr(self, field_def.name)
             if value is not None or field_def.name in _ALWAYS_EMIT: