add Baranov catch equation

[klsys]

Implementation of the Baranov catch equation in FLBEIA (as demonstrated in ICES WGMIXFISH-METHODS 2025 meeting)

• implemented for "fixedEffort" and "SMFB" fleets ("min", "max")
• only supports for single area and single season operating models; multiple iterations possible
• for SMFB fleets
  1. solve a set of nonlinear equations for a given set of chokes species
  2. check stop conditions (each SMFB fleet needs to have a full uptake of at least one quotum) (not overshooting (min) /undershooting (max) other quota)
  3. update candidate choke stocks
  4. rerun i. to iii. until stop conditions satisfied (while loop)
• for "fixedEffort" fleets, effort is a priori known (and independent from fishing opportunities), catches can be computed if effort for all fleets is known
• depends on nleqslv package
• currently no cases identified where the while loop was not finished, but need to define some safeguard stop condition to avoid an infinite loop
• support for both catch and landings targets
• no support for catch/landings thresholds compared to i.e. stock numbers