Separate client and server APIs into two separate packages

Right now, the NuGet package (ModelContextProtocol) contains both the client and the server APIs. There are scenarios where just the client is needed, but that pulls-in server specific dependencies, e.g. dependencies on the ASP.NET DI container abstractions which are not used in many client apps (non ASP.NET).

It would be great to break the package into two, e.g.
ModelContextProtocol.Client
ModelContextProtocol.Server