Use Kraus formalism for dynamic circuits on `braket_dm`

**Describe the feature you'd like**
Implement dynamic circuits on `braket_dm` using the Kraus formalism by default (instead of the existing branched method).

**How would this feature be used? Please describe.**
This is just a more efficient dynamic circuit simulation method when we're already working with density matrices.

**Describe alternatives you've considered**
We already support dynamic circuits on `braket_dm` via branched execution