Collisions with uneven weights "works" but gives wrong values

[rfbird]

Right now the TA collisions accepts a users requests to run collisions on species with different weights. This runs but does not give a correct science answer as it is not supported by the current formulation of the TA operator

There is theory work by Miller and Combi that addresses this, but needs to be implemented

For now we can just detect the bad input and error out to avoid the impression that the code is doing the right thing when it's not

[rfbird]

This now tries to give a warning if it can detect the issue, but is not robust