Volume for hypothesis

This PR adds a Docker volume for the ./.hypothesis folder that gets generated by the test suite upon make test.

Since the tests are run as root in the container, the suite creates a ./.hypothesis folder in the repo folder. This folder is owned by root, which means a dev needs to sudo make test or sudo docker-compose run test on subsequent runs.

Adding the volume sequesters the contents of the ./.hypothesis folder to make testing less annoying while retaining it for future tests.