difftest core: Amend diff model with throttle changes (normal operation)

[danwt]

Problem

The slash throttle PR changes the way things work under normal operation (and abnormal operation). The diff test model should be changed to account for this.

Closing criteria

Update the diff test core model so that the tests pass using the throttle when the Replenish Period and Allowance params are large.

Problem details

The throttle should work almost as normal when the slash allowance is very large.

TODOs

• Labels have been added for issue
• Issue has been added to the ICS project

[danwt]

cc @smarshall-spitzbart

[shaspitz]

Looks good, this issue is about using diff tests as a regression test, and will need to be fixed before #462 is merged. Whereas #534 is future work to test the throttling logic (not regression testing)