MEDYAN.fila_load_force
Tuple{MEDYAN.Context, MEDYAN.FilaTipIdx}
Return the end load force for the given filament tip in pN.
Values are always ≥ 0: the compressive force component pushing inward on the tip projected along the filament axis.
Load forces are computed during minimize_energy! and baoab!. They are zero before the first mechanics cycle and after filament creation.
These load forces slow polymerization/depolymerization rates via a Boltzmann factor exp(-β × spacing × load_force).