refactor: simplify generated python code (#558)

templates/components/loaders/python/file/loader.py

templates/components/vectordbs/python/mongo/constants.py

templates/components/vectordbs/python/mongo/generate.py

templates/components/vectordbs/python/mongo/settings.py

templates/components/vectordbs/python/none/constants.py

templates/components/vectordbs/python/none/generate.py

templates/components/vectordbs/python/none/index.py

templates/components/vectordbs/python/none/settings.py

templates/components/vectordbs/python/pg/constants.py

templates/components/vectordbs/python/pg/generate.py

templates/components/vectordbs/python/pg/index.py

templates/components/vectordbs/python/pg/settings.py

templates/components/vectordbs/python/pinecone/constants.py

templates/components/vectordbs/python/pinecone/generate.py

templates/components/vectordbs/python/pinecone/settings.py

templates/types/simple/fastapi/app/engine/__init__.py

templates/types/simple/fastapi/app/settings.py

templates/types/simple/fastapi/main.py

templates/types/streaming/fastapi/app/engine/__init__.py

templates/types/streaming/fastapi/app/settings.py