Consider using pre-calculated t12 / t21 values

[ashiklom]

In PROSPECT, for a given refractive index, the t12 and t21 values are completely independent of the PROSPECT parameters.

https://github.com/RemoteSensingTools/CanopyOptics.jl/blob/main/src/core/prospect.jl#L57

The computational impact here is minuscule, but if you're looking to shave a few extra nanoseconds off the execution (especially for iterative PROSPECT inversion; this may also slightly streamline the automatic differentiation), you can pre-calculate t12 and t21 for default values of the refractive index in loadProspect.jl and pass those fixed quantities to the remaining PROSPECT routines.

Something to consider.