[Bug]: controller: include the unset sweep_config state in its return annotation

Describe the bug

The controller returned by wandb.controller() declares sweep_config -> dict | sweeps.SweepConfig, but returns None during its supported deferred-creation lifecycle. This remains true after configuring search and metric, before a sweep has been created/read.

The constructor initializes the backing field to None and explicitly supports deferred creation. The public property returns that state unchanged. The adjacent sweep_id property already includes None.

Local reproduction

Install the optional sweeps package. The API factory below is simulated to avoid authentication; no controller fields or methods are replaced and no API methods are called.

from unittest.mock import patch
import inspect
import wandb

with patch("wandb.Api") as api:
    controller = wandb.controller()
    print(inspect.signature(type(controller).sweep_config.fget))
    print(controller.sweep_config)
    controller.configure_search("random")
    controller.configure_metric("loss")
    print(controller.sweep_config)
    assert not api.return_value.method_calls

(self) -> 'dict | sweeps.SweepConfig'
None
None

Mypy accepts wandb.controller().sweep_config.get("metric"), which fails in this supported state.

Expected behavior

Represent the unset state in the property's return contract, without requiring creation of a remote sweep just to inspect a newly configured controller.

Environment

• W&B SDK: 0.30.0; also reproduced on main 8f93d444e29e4d1a50a888899f51051012ee2679
• Python: 3.12.12; sweeps: 0.2.0; mypy: 2.3.1
• OS: macOS 26.1, arm64
• W&B server: not applicable to local checks