Important

Add GCPVertexGeminiSFTConfig to OptimizationConfig and update tests and deserialization to support it.

• Behavior:
  • Add GCPVertexGeminiSFTConfig to OptimizationConfig in __init__.py for Python client visibility.
  • Update deserialize_optimization_config in pyo3_helpers.rs to handle GCPVertexGeminiSFTConfig.
• Tests:
  • Add test_sync_gcp_vertex_gemini_sft and test_async_gcp_vertex_gemini_sft in test_optimization.py for new config.
• Misc:
  • Update error message in deserialize_optimization_config to include GCPVertexGeminiSFTConfig.

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