Merge remote-tracking branch 'origin/main' into 169.lease-maint-from-config

docs/source/designs/costs.rst

src/_zkapauthorizer/_storage_client.py

src/_zkapauthorizer/_storage_server.py

src/_zkapauthorizer/storage_common.py

src/_zkapauthorizer/tests/strategies.py

src/_zkapauthorizer/tests/test_storage_protocol.py