Fix issue where _simulateTemps may never reach target temp

[kantlivelong]

What does this PR do and why is it necessary?

When setting temperatures whilst using the Virtual Printer there is a chance the target is never truly reached but is instead within ~0.5C. This handles the condition where the temperature difference is less than the delta and makes the next temperature change equal to the difference.

How was it tested? How can it be tested by the reviewer?

1. Set target temperature
2. Wait (Note: It seems that target temp may be reached if sitting in a breakpoint and that is because of the timeDiff calculation)
3. Observe

Any background context you want to provide?

What are the relevant tickets if any?

Screenshots (if appropriate)

Further notes