Use dev-dependencies

[Froxcey]

• Move some dependencies to dev-dependencies
• Remove subpackage

[Froxcey]

Why: Multichat only use those dependencies for types and tests under the hood. The actual clients are provided by downstream in production and uses dependency injection. It would be stupid to install millions of packages when the downstream only want to attach, for example, the djs client to Multichat. Maintainers can install dev-dependencies to get the nice type annotations and use it for tests, and downstream users can select which client to install and shrink the dependency tree.