most of the way to storing unblinded tokens and generating pass later

docs/source/configuration.rst

src/_zkapauthorizer/_plugin.py

src/_zkapauthorizer/_storage_client.py

src/_zkapauthorizer/controller.py

src/_zkapauthorizer/tests/strategies.py

src/_zkapauthorizer/tests/test_client_resource.py

src/_zkapauthorizer/tests/test_plugin.py

src/_zkapauthorizer/tests/test_storage_protocol.py