The parameter KHTR_USE_EBT_STRUCT was introduced with an incorrect
variable name within the local control structure. The variable was
named KhTh_use_ebt_struct, indicating thickness diffusivity, instead
of the correct KhTr_use_ebt_struct, which indicates tracer diffusivity.
This commit rectifies the naming inconsistency.

This commit introduces a new parameter, FULL_DEPTH_KHTR_MIN, which
enforces a user-specified minimum diffusivity (KHTR_MIN) to be
applied throughout the entire water column, instead of only at
the surface. This option is available only when
KHTR_USE_EBT_STRUCT=True and KHTR_MIN > 0.

This commit introduces a new parameter, FULL_DEPTH_KHTH_MIN, which
enforces a user-specified minimum diffusivity (KHTH_MIN) to be
applied throughout the entire water column instead of only at
the surface. This option is available only when
KHTH_USE_EBT_STRUCT=True and KHTH_MIN > 0.