Flattened Dimension bounds become ndarrays of a single value instead of floats/ints

[lebrice]

Describe the bug When the space is transformed (e.g. when <AlgoClass>.requires_shape == "flattened"), the bounds of the resulting space dimensions are ndarrays of a single value, which is inconsistent IMO.

Expected behavior Expect the bounds() of the flattened Dimensions to be floats / ints, not ndarrays.