fix: support PyPI jupyter-kernel-client>=1.0 (JupyterKernelClient rename)

[theaathish]

Problem

Installing from PyPI (uv tool install google-colab-cli / pip install google-colab-cli) resolves the unpinned jupyter-kernel-client dependency to 1.0.2, where KernelClient was renamed to JupyterKernelClient.

colab exec then fails on any session (auth + colab status/colab ls still work):

AttributeError: module 'jupyter_kernel_client' has no attribute 'KernelClient'

Full traceback originates at src/colab_cli/runtime.py in ColabRuntime.kernel_client (jupyter_kernel_client.KernelClient(...)).

Repro (CLI 0.6.0 + PyPI jupyter-kernel-client 1.0.2):

colab status   # OK - shows session, IDLE
colab ls       # OK
echo "print('hi')" | colab exec   # AttributeError above

Fix

Resolve the client class across all known variants in ColabRuntime.kernel_client:

• ColabKernelClient(proxy_token=...) (git fork version)
• KernelClient(token=...) (PyPI <1.0)
• JupyterKernelClient(token=...) (PyPI >=1.0, fallback)

The JupyterKernelClient constructor is compatible (passes through to KernelHttpManager via **kwargs: server_url, token, kernel_id, client_kwargs, headers), verified live with colab exec after patching.

Tests

• Updated test_colab_runtime_kernel_client to handle all three variants.
• Added test_colab_runtime_kernel_client_jupyterclient_fallback simulating PyPI>=1.0 (only JupyterKernelClient present).
• uv run pytest tests/test_runtime.py -v: 9 passed.
• uv run ruff check + ruff format --check: clean.
• Live: echo "print('connection_test_ok')" | colab exec → connection_test_ok.

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