[bastion] Fix KeyError when enableTunneling is absent from bastion API response

[Copilot]

az network bastion ssh, rdp, and tunnel commands crash with KeyError: 'enableTunneling' when the bastion host's API response omits that property (e.g., Standard SKU with tunneling not explicitly configured).

Changes

• _is_nativeclient_enabled: bastion['enableTunneling'] → bastion.get('enableTunneling', False)
• rdp_bastion_host and create_bastion_tunnel: same fix for the inline SKU+tunneling guards that bypass _is_nativeclient_enabled
• New unit tests (test_bastion_unit.py): covers all SKU variants including the missing-key regression case

Related command

az network bastion ssh / az network bastion rdp / az network bastion tunnel

General Guidelines

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• Have you run python scripts/ci/test_index.py -q locally? (azdev required; see .azure-pipelines/templates/azdev_setup.yml for the install command until azdev==0.2.11b1 is on PyPI)
• My extension version conforms to the Extension version schema

For new extensions:

• My extension description/summary conforms to the Extension Summary Guidelines.

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[azure-client-tools-bot-prd]

️✔️Azure CLI Extensions Breaking Change Test

️✔️Non Breaking Changes

[azure-client-tools-bot-prd]

Hi @copilot,
Please write the description of changes which can be perceived by customers into HISTORY.rst.
If you want to release a new extension version, please update the version in setup.py as well.

[yonzhan]

bastion