fix(transport): ping 容错 TdxConnectionError，避免单台服务器拖垮测速

ping_host 仅 except OSError，但握手期 _recv_exact_sock 抛的 TdxConnectionError
继承自 TdxError(Exception) 而非 OSError，逃出捕获后经 ping_all 的 fut.result()
重新抛出，导致非交易时间服务器 accept 后立即 FIN 时整个 easy-tdx ping 崩溃。
- ping_host: except (OSError, TdxConnectionError)，对齐 docstring 返回 None
- ping_all: fut.result() 加 try/except 防御层，单 host 失败只跳过不崩
- 新增 2 例回归测试

tests/unit/test_sync_transport.py

@@ -3,7 +3,7 @@
 from unittest.mock import patch
 
 from easy_tdx.exceptions import TdxConnectionError
-from easy_tdx.transport.sync import TdxConnection
+from easy_tdx.transport.sync import TdxConnection, ping_all, ping_host
 
 
 class _FakeSocket:
@@ -18,6 +18,9 @@ class _FakeSocket:
     def connect(self, address: tuple[str, int]) -> None:
         self.connected_to = address
 
+    def sendall(self, data: bytes) -> None:
+        pass
+
     def close(self) -> None:
         self.closed = True
 
@@ -45,3 +48,41 @@ def test_sync_connection_closes_socket_when_setup_fails() -> None:
     assert sock.connected_to == ("127.0.0.1", 7709)
     assert sock.closed is True
     assert conn._sock is None
+
+
+def test_ping_host_returns_none_when_server_closes_during_handshake() -> None:
+    """握手期服务器关闭连接（_recv_exact_sock 抛 TdxConnectionError）应返回 None。
+
+    回归：ping_host 旧版仅 except OSError，未捕获 TdxConnectionError（继承自
+    TdxError(Exception) 而非 OSError），导致单个服务器握手失败就让整个
+    ping_all / `easy-tdx ping` 命令崩溃。非交易时间服务器 accept 后立即 FIN
+    时必现。
+    """
+    sock = _FakeSocket()
+    with (
+        patch("easy_tdx.transport.sync.socket.socket", return_value=sock),
+        patch(
+            "easy_tdx.transport.sync._recv_exact_sock",
+            side_effect=TdxConnectionError("连接被服务器关闭"),
+        ),
+    ):
+        result = ping_host("192.0.2.1", port=7709, timeout=0.2)
+
+    assert result is None
+    assert sock.closed is True
+
+
+def test_ping_all_skips_handshake_failure_without_crash() -> None:
+    """ping_all 中任一服务器握手失败（TdxConnectionError）应被跳过，不崩溃。"""
+
+    def fake_ping(host: str, port: int, timeout: float) -> float | None:
+        if host == "bad":
+            raise TdxConnectionError("连接被服务器关闭")
+        return 0.05
+
+    with patch("easy_tdx.transport.sync.ping_host", side_effect=fake_ping):
+        results = ping_all(hosts=["good", "bad"], port=7709, timeout=0.2)
+
+    hosts_ok = [h for h, _ in results]
+    assert "good" in hosts_ok
+    assert "bad" not in hosts_ok