Extract shared Behave step definitions for LLM provider tests into
provider_shared_steps.py to eliminate duplicate @given registrations
that caused AmbiguousStep errors across anthropic, google, and openai
provider step files. Add missing step definitions to
consolidated_ai_models_providers_steps.py for consolidated feature
scenarios. Add @given decorator alongside @when for provider creation
steps used as Given steps in feature files.
HAL9000