Make difference module handle circular cubes (metoppv#2016)

* Resolved merge conflict

* Added another failing test for difference module. Differences calculated correctly but need to add extra dimension for the wrap-around distance.

* Resolved merge conflicts

* Auto-formatting

* Import Bugfix

* Ran isort against spatial.py

* Added test for appropriate error for unhandled cubes and made code match it.

* iSort on spatial.py again

* Another attempt at autoformatting

* Tidied up

* Removed confusing variable name

* Autoformatting

* Tried manually sorting import order as isort still failing in github actions despite running locally and pushing

* And again

* And again

* Linting suggestion

* Review Actions

* Ran isort to fix gha

* Added test for cubes with flipped axes (lonitude increasing along columns not rows and vice versa for latitude). Fixed code to handle this case.

* black, isort, flake8

* Ran isort in isolation

* Fixed test failures resulting from breaking changes made by upstream PR

* Black

* updates as per review comments and adds test for 0-360 degree case

* update comment

* formatting

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Co-authored-by: Marcus Spelman <[email protected]>