Support binary operations e.g. arctan2 division

[sadielbartholomew]

(Summarising DH/SB discussions today) element-wise binary operations i.e. operations combining two operands, are not trivial to implement with LAMA, unlike unary operations which are so & are already handled via LAMA in the codebase. We decided to think about & investigate efficient means to partition element-wise binary operations with LAMA towards adding logic to do so for a version after the imminent 3.2.0, ideally 3.3.0.

In particular, I recently implemented (fully except for LAMA management) the two-argument inverse tangent method arctan2(y, x) which takes two data arrays as inputs and as a first step takes the element-wise quotient. As this needs such two-input LAMA logic, I have commented it out (tagged with AT2) pending that, so arctan2 i.e. division would be the natural case for experimentation.

We can then as appropriate add in further binary methods, though a different LAMA strategy could perhaps optimise (serially) any one case.