Add a property flag in `kraus_op` to identify whether it is a 'scaled' unitary matrix

[1tnguyen]

Description

Kraus operators can be categorized into (1) probabilistic unitary application (e.g., depolarizing) or (2) non-unitary matrix application (e.g., amplitude damping).

This PR adds a property flag and a utility function to categorize Kraus operators. Also, added a unit test to verify the correctness of the check.