Processes a ChainNode: RType#BinaryOp, RType#Pipe, and magrittr-style %op% calls
(infix-special RType#FunctionCalls) all nest on their left operand, so a long a + b + c + ... or
a %>% f() %>% f() %>% ... chain buries it arbitrarily deep.
This walks the left spine of chain nodes with an explicit loop (bounded stack usage regardless of
chain length), processes the innermost (leftmost) node normally, and then folds outward: each level's left
operand is wrapped via processFunctionArgument.
Processes a ChainNode: RType#BinaryOp, RType#Pipe, and magrittr-style
%op%calls (infix-special RType#FunctionCalls) all nest on their left operand, so a longa + b + c + ...ora %>% f() %>% f() %>% ...chain buries it arbitrarily deep. This walks the left spine of chain nodes with an explicit loop (bounded stack usage regardless of chain length), processes the innermost (leftmost) node normally, and then folds outward: each level's left operand is wrapped via processFunctionArgument.