Make it possible to use generic evaluator in multi component fields

[smolins]

Generic evaluators allow for a convenient way to consider simple reactions but in problems with more than one solute this is not possible because generic evaluators cannot be applied to multicomponent fields.

The 2 tracer example from transport in the short course

https://github.com/amanzi/ats-short-course/blob/ats-short-course-20250908/03_transport/.transport_solution.xml

had to be simplified to a 1 tracer problem for tracer2

https://github.com/amanzi/ats-short-course/blob/ats-short-course-20250908/04_reactive_transport/transport_tracer.xml

before a first order decay could be applied to tracer 2.

https://github.com/amanzi/ats-short-course/blob/ats-short-course-20250908/04_reactive_transport/first-order_tracer.xml