Support for numerical comparisons in `Op` type

[stephancill]

Mod currently supports the following Ops

type Op = {
    AND?: Op | Op[];
    OR?: Op[];
    NOT?: Op | Op[];
    equals?: string;
    oneOf?: string[];
    notOneOf?: string[];
    contains?: string;
    startsWith?: string;
    endsWith?: string;
    regex?: string;
};

It is missing numerical comparators such as greaterThan, greaterThanOrEquals, lessThan, lessThanOrEquals