Feature request: Allow services to be shared across wireit invocations

In some projects I might have many entrypoints into my script graph that share a common service. I might want to invoke these entrypoints separately while having them share that single service.

An example is the Firebase emulator. Generally a project has s single emulator config which supplies it with settings including ports to use. Starting the emulator multiple times isn't possible because of the fixed port. It's also a stateful service, so even if you solve the port issue you might want entrypoints to share the same state.

The entrypoints might be an app server, a separate dev server for component stories, and test entrypoints, which all need access to the emulator. I want to be able to run tests while the app server is running, or run app and stories servers.