refactor(pypi): convert to class-based (#11064)

lib/datasource/api.ts

lib/datasource/metadata.spec.ts

lib/datasource/pypi/index.spec.ts

lib/datasource/pypi/index.ts

lib/manager/pip_requirements/extract.ts

lib/manager/pip_setup/extract.ts

lib/manager/pipenv/extract.ts

lib/manager/poetry/extract.ts

lib/manager/setup-cfg/extract.ts

lib/workers/repository/init/vulnerability.ts

lib/workers/repository/process/lookup/index.spec.ts