use refs for long variable names

[juliasloan25]

To make code more readable while avoiding extra allocations, we should use refs at the beginning of functions. This is done in oceananigans.

E.g. we could create a ref for rho_flux_h_tot at the beginning of this function and use it here

To Do

• find other instances of long names that can be shortened in functions, primarily in these folders:
  • experiments/AMIP/components/...
  • src/...
  • maybe more places?
• add local refs for these and use them inside functions
• verify no behavioral changes