feat: encoder types

semantic_router/encoders/__init__.py

semantic_router/encoders/aurelio.py

semantic_router/encoders/base.py

semantic_router/encoders/bedrock.py

semantic_router/encoders/bm25.py

semantic_router/encoders/clip.py

semantic_router/encoders/cohere.py

semantic_router/encoders/fastembed.py

semantic_router/encoders/google.py

semantic_router/encoders/huggingface.py

semantic_router/encoders/mistral.py

semantic_router/encoders/openai.py

semantic_router/encoders/tfidf.py

semantic_router/encoders/vit.py

semantic_router/encoders/zure.py

semantic_router/routers/base.py

semantic_router/routers/hybrid.py

semantic_router/routers/semantic.py

tests/integration/encoders/test_openai_integration.py

tests/unit/encoders/test_base.py