chore(smolagents): CI Failures For Smolagents

[ialisaleh]

Closes #2561

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Note

Stabilizes LiteLLM-related tests by removing external dependency on tiktoken network access.

• Adds patch_tiktoken_encoding pytest fixture that mocks tiktoken.get_encoding to return a dummy encoder
• Wires the fixture into test_litellm_reasoning_model_has_expected_attributes
• Imports MagicMock and patch to support the mock

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