Introduce METHOD_FIBER type and FIBER_PRIMITIVE/DEF_FIBER_PRIMITIVE macros to handle primitives that directly manipulate the fiber's call stack, eliminating the need for the special NO_VAL return value hack. Remove all fn_call0 through fn_call8 primitives and convert them to fiber primitives that call callFunction without returning a value. Update Primitive typedef to remove the Fiber parameter, and adjust primitive_metaclass_new and the interpret switch case accordingly. Delete the NO_VAL macro and its TODO comment from value.h.
