Integration Method in next_state

[teubert]

Requirement Text
Update integration method to apply in next_state instead of simulate_to* (Idea from NGC). Integration method can be set at initialization or afterwards

Background Information
Currently, the supported integration methods are euler and rk4. These integration methods are applied in simulation by changing the integration_method argument. They do not apply in next_state, which means they are not applied by particle filters or other methods that use next_state directly.

Suggested Solution
Override next_state method for only discrete models to selected integration method.

DoD
edit this to be a list of tasks that need to be completed

• Implement feature
• Add tests
• update documentation
• Add to change notes for next release