stockflows assume ternary+ operators can be expressed as distributive binary

[neonWhiteout]

Notice there are two f under op, when we're only applying it once.
As we don't currently expect any operands with arity > 2, not yet an issue.

[Saityi]

Additional info: This is currently allowed to handle how Julia represents + and * in a lisp-like way, e.g., the expression tree of v = a + b + c + d * e * f * g appears in lisp notation as (+ a b c (* d e f g)). It assumes any function with arity > 2 is one of those two and rearranges it into a form accepted as a StockAndFlowF, such as, for the previous example,

v    = a + b + c + d * e * f * g
# becomes
tmp1 = a + b
tmp2 = tmp1 + c
tmp3 = d * e
tmp4 = tmp3 * f
tmp5 = tmp4 * g
v    = tmp5 + tmp2

(or some such)

(That is to say, we do often see functions with arity > 2: + & *)

An easy solution might be to restrict when this kicks in to just specific functions, and reject anything else of arity > 2.