chore: add docstrings for indexes and routers

semantic_router/index/base.py

semantic_router/index/hybrid_local.py

semantic_router/index/local.py

semantic_router/index/pinecone.py

semantic_router/index/postgres.py

semantic_router/index/qdrant.py

semantic_router/routers/base.py

semantic_router/routers/hybrid.py

semantic_router/routers/semantic.py