Recursive bitwise operation on MaskGroup

[jacanchaplais]

Description

Currently performing a bitwise operation with MaskGroup instances returns a MaskArray, losing all nesting information. Would be good to have a recursive update over the MaskGroup.

Potential problem

The order of precedence for a bitwise operation between two MaskGroup instances would then become ambiguous. Which nesting structure should be preserved?

Potential solution

Could form a new MaskGroup, which contains both of the inputs, with agg_op defined to the relevant bitwise operation. This would preserve the structure, and deliver the desired behaviour, but would increase levels of nesting, and if users wanted to select out individual MaskArray objects, they would not have the masking applied.

Ideas need to be fleshed out more. Will place this on the backlog for future development.