Add arrayFold function for multi-array lambda accumulation

Why it matters

This feature enables users to perform fold (reduce) operations on multiple arrays simultaneously. It solves the problem of aggregating values across several arrays in a single pass, providing more expressive and efficient data transformations.

How to use it

Use arrayFold by passing an accumulator variable, a lambda function describing the folding logic, an initial accumulator value, and one or more arrays of equal cardinality. The syntax is:

arrayFold(accumulator, x1, ..., xn -> expression, initial, array1, ..., arrayn)

where accumulator is the variable holding the folding result, x1, ..., xn are elements of the arrays being folded, and initial is the starting value.