Package project with Coherent #558

In #516, importlib_metadata was caught in the packaging bootstrap problem. Currently, the only demonstated solution/workaround for the problem is to adopt a build system that can produce sdists that depend only on the most minimal build system with no dependencies (flit). Since this project doesn't want to adopt flit directly (and the additional maintenance burden that implies), this project should instead move to the Coherent Build System, which has most of the benefits of the skeleton-based approach while also compiling to flit sdists. Let's explore migrating to that system.