Add return typehints to sample_ functions

Most sample functions (eg. def sample_ising) return a Future object.

Calls to these functions should use typehints to indicate the return types

ex. Look to sample_problem, it does use the typehint:

def sample_problem(self,
problem: Any,
*,
label: str | None = None,
problem_type: str | None = None,
upload_params: dict | None = None,
**sample_params: Any,
) -> Future: