fix(honcho): bound the shutdown flush by the shutdown deadline

Provider shutdown handed the manager a remaining budget, but flush_all ran first with no deadline and blocked on each session's flush lock. An async upload still in flight held that lock, so shutdown waited the full HTTP timeout past its declared budget. flush_all and the queue drain now take the deadline, skip a session whose lock or budget is gone, and log one warning with the count of messages that stayed unsynced.

tests/honcho_plugin/test_async_memory.py

@@ -377,14 +377,14 @@ class TestStopAsyncWriterDrain:
         assert flushed == ["after"]
         assert mgr._async_queue.empty()
 
-    def test_shutdown_passes_the_join_timeout_through(self, make_manager, monkeypatch):
+    def test_shutdown_gives_the_writer_join_what_the_flush_left_of_the_timeout(self, make_manager, monkeypatch):
         mgr = make_manager("async")
         seen = {}
         monkeypatch.setattr(mgr, "stop_async_writer", lambda timeout=10.0: seen.setdefault("timeout", timeout))
 
         mgr.shutdown(timeout=2.5)
 
-        assert seen["timeout"] == 2.5
+        assert 2.0 < seen["timeout"] <= 2.5
 
 
 class TestAsyncWriterRetry: