Regex Tester & Validator

Matches multiplication expressions between two arrays of numeric literals, such as `[1,2,3] * [4,5,6]` or `[1.5, 2] x [3, 4.5]`. Each array must contain one or more integers or decimal numbers separated by commas with optional whitespace, and the operator can be either `*` or `x`. With the gm flags, it validates these matrix/vector-style expressions line-by-line, making it useful for parsing math syntax in DSLs, calculators, or lightweight expression evaluators.