feat: support for python 3.9

coverage.xml

docs/encoders/fastembed.ipynb

docs/encoders/huggingface.ipynb

poetry.lock

pyproject.toml

replace.py

semantic_router/encoders/__init__.py

semantic_router/encoders/bm25.py

semantic_router/encoders/huggingface.py

semantic_router/encoders/openai.py

semantic_router/hybrid_layer.py

semantic_router/layer.py

semantic_router/llms/openai.py

semantic_router/llms/openrouter.py

semantic_router/route.py

semantic_router/schema.py

semantic_router/utils/llm.py

tests/unit/encoders/test_bm25.py

tests/unit/encoders/test_huggingface.py

tests/unit/test_hybrid_layer.py