Context decorator

[slinkydeveloper]

It is a common practice in Typescript to carry around a "context" object containing all the code dependencies. Because we have already our own context, people doing that will need to wrap our context in their context.

It would be nice to support this use case better, autowrapping somewhat like this:

const obj = object({ 
  name: "MyObj",
 
  makeContext: (restateCtx) => MyCtx { restateCtx },

  handlers: {
    myObjHandler: async (ctx: MyCtx<ObjectContext>): Promise<string> => {
      // handler code
    },
    myObjHandler: restate.handlers.shared(async (ctx: MyCtx<ObjectSharedContext>): Promise<string> => {
      // handler code
    })
  },
})

Some notes:

• I guess the constraint will be anyway that the custom user context type needs to have a generic that supports restate context?
• How to get the typing right -> if the user provides this makeContext, the handlers type need to infer the wrapped type?
• How we deal with the different context types (shared/exclusive in object for example)
• How we do this without breaking the client type magic stuff.

cc @nikrooz