lint and test fix

semantic_router/layer.py

semantic_router/llms/__init__.py

semantic_router/llms/base.py

semantic_router/llms/cohere.py

semantic_router/llms/openai.py

semantic_router/llms/openrouter.py

semantic_router/schema.py

semantic_router/utils/function_call.py

tests/unit/llms/test_llm_cohere.py

tests/unit/llms/test_llm_openai.py

tests/unit/llms/test_llm_openrouter.py

tests/unit/test_route.py

tests/unit/test_schema.py