Tempering during adaption is unstable

[xukai92]

We need to disable tempering during adaption. How? Possible options

1. Force to use normal leapfrog during adapation.

• This is not generic as we may introduce other integrator in the future which can acutally be used during adaption
• But this would be easy to implment for now

2. amend TemperedLeapfrog to have a flag which indicates if it's in adpation phase

• We need to set and re-set this flag before and after adaption

3. Any other proposal?

[yebai]

Force to use normal leapfrog during adapation.

I think we can always use normal leapfrog during adaption for now. I'm happy to change this to an alternative, improved option in the future.