Enhance GatewayClient

[vincentye38]

• Removed kernel_id parameter from GatewayClient ctor because its supper class's ctor doesn't have this parameter. When a kernel manager try to instantiate an object of it, it doesn't know GatewayClient is the concrete class and It need to pass kernel_id to the ctor. Thus, It fails with the following error message. kernel_id is only for constructing ws_url (gateway websocket url.) Replace kernel_id with ws_url property. So the kernel manager can set ws_url instead of kernel id.
  The kernel_id parameter caused the following exception when the ctor is called by self.kernel_client = self.client(session=self.session) in KernelManager.init

[W 2026-02-18 18:31:50.832 ServerApp] wrote error: "GatewayKernelClient.__init__() missing 1 required positional argument: 'kernel_id'"
    Traceback (most recent call last):
      File "/Users/xiang_ye/github/aiml-jupyter-server/jupyter_server/services/sessions/handlers.py", line 90, in post
        s_model = await sm.create_session(
                  ^^^^^^^^^^^^^^^^^^^^^^^^
      File "/Users/xiang_ye/.conda/envs/saturn/lib/python3.11/site-packages/jupyter_server_documents/session_manager.py", line 249, in create_session
        session_model = await super().create_session(
                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      File "/Users/xiang_ye/github/aiml-jupyter-server/jupyter_server/services/sessions/sessionmanager.py", line 286, in create_session
        kernel_id = await self.start_kernel_for_session(
                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      File "/Users/xiang_ye/github/aiml-jupyter-server/jupyter_server/services/sessions/sessionmanager.py", line 359, in start_kernel_for_session
        kernel_id = await self.kernel_manager.start_kernel(
                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      File "/Users/xiang_ye/github/aiml-jupyter-server/jupyter_server/services/kernels/kernelmanager.py", line 233, in _async_start_kernel
        kernel_id = await self.pinned_superclass._async_start_kernel(self, **kwargs)
                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      File "/Users/xiang_ye/.conda/envs/saturn/lib/python3.11/site-packages/jupyter_client/multikernelmanager.py", line 263, in _async_start_kernel
        km, kernel_name, kernel_id = self.pre_start_kernel(kernel_name, kwargs)
                                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      File "/Users/xiang_ye/.conda/envs/saturn/lib/python3.11/site-packages/jupyter_client/multikernelmanager.py", line 209, in pre_start_kernel
        km = self.kernel_manager_factory(
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      File "/Users/xiang_ye/.conda/envs/saturn/lib/python3.11/site-packages/jupyter_client/multikernelmanager.py", line 87, in create_kernel_manager
        km = kernel_manager_ctor(*args, **kwargs)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      File "/Users/xiang_ye/.conda/envs/saturn/lib/python3.11/site-packages/nextgen_kernels_api/services/kernels/kernelmanager.py", line 47, in __init__
        self.kernel_client = self.client(session=self.session)
                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      File "/Users/xiang_ye/.conda/envs/saturn/lib/python3.11/site-packages/jupyter_client/manager.py", line 740, in client
        return super().client(**kwargs)  # type:ignore[return-value]
               ^^^^^^^^^^^^^^^^^^^^^^^^
      File "/Users/xiang_ye/.conda/envs/saturn/lib/python3.11/site-packages/jupyter_client/manager.py", line 277, in client
        return self.client_factory(**kw)
               ^^^^^^^^^^^^^^^^^^^^^^^^^
      File "/Users/xiang_ye/.conda/envs/saturn/lib/python3.11/site-packages/jupyter_server_documents/kernel_client.py", line 46, in __init__
        super().__init__(*args, **kwargs)
      File "/Users/xiang_ye/.conda/envs/saturn/lib/python3.11/site-packages/nextgen_kernels_api/services/kernels/client.py", line 87, in __init__
        super().__init__(*args, **kwargs)
    TypeError: GatewayKernelClient.__init__() missing 1 required positional argument: 'kernel_id'

• added an logic to reconnect to remote gateway if the connection dropped.

[vincentye38]

Note: kernel_id is only used for constructing gateway websocket url.

[vincentye38]

Note: I proposed to move ws_url initialization to kernel manager, and make ws_url as a property of kernel client. Because kernel manager is responsible to start kernel process, instantiate a kernel client to connect o the process. So it knows information of how to connect to the kernel process.
Kernel manager will set ws_url of kernel client after it creates the kernel client.