🏷️ fix(strongly-typed) allow use of generic helpers

[alecgibson]

Fixes #170

At the moment it's impossible to create generic helper functions to deal with TypedContainer:

interface MyMap {
  foo: string;
}

function fn<T extends MyMap>(container: TypedContainer<T>) {
  container.get('foo') // error
}

This is because of the Synchronous type that guards against calling .get() on Promise bindings. Under the hood, this type is a mapped type, which doesn't work well with generics (by design).

Rather than drop this guard all together, this change aims to strike a balance by removing the Synchronous mapped type, and instead changing the return type of synchronous get() methods to be never if the binding is a Promise.

This won't error as obviously or as immediately as before, but will still at least flag to the developer semantically that this binding will never return a value (since it will throw), and should cause compilation errors if consumers try to do anything with the returned value.

In return, we gain the ability to use generic helper functions.