C8: skip non-kline frames in the live_trading example

The combined Binance stream interleaves the kline payloads with
subscription acks, heartbeats and error objects. The example pulled
k = payload.get("k", {}) and immediately did float(k.get("c")) — for
any non-kline frame k is {}, k.get("c") is None, and float(None) raises
TypeError, crashing the script the moment it connects.

Skip frames without a kline payload (no "k" object, or no "c" close
field) with a debug log line, matching the C2 fix on the Rust adapter.

examples/python/live_trading.py

@@ -96,6 +96,12 @@ async def run(symbol: str, interval: str) -> None:
             envelope = json.loads(raw)
             payload = envelope.get("data", {})
             k = payload.get("k", {})
+            if not k or "c" not in k:
+                # Subscription acks, heartbeats and error frames carry no
+                # kline payload — skip them instead of crashing on
+                # float(None) the moment the stream opens.
+                log.debug("skipping non-kline frame: %s", raw)
+                continue
             close = float(k.get("c"))
             is_closed = bool(k.get("x"))
             snap = state.update(close)