Pure doctests

[pp-mo]

Description

A so-far highly sketchy look at what it might take to adopt the intended future "doctest runner" from ncdata into Iris.

In practice, the doctest-runner code should go into a shared template.

In short:

• It decouples the doctests from Sphinx, and make them much faster + can run just the ones you want.
• But it means a fair bit of work re-formatting as the existing testsetup/testcleanup sections are in a Sphinx-specific format.
  • ..and the functionality isn't the same either.

[scitools-ci]

Templating

This PR includes changes that may be worth sharing via templating. For each file listed below, please either:

• Action the suggestion via a pull request editing/adding the relevant file in the SciTools/.github templates/ directory. ¹
• Raise an issue against the SciTools/.github repo for the above action if you really don't have 10mins spare right now. Include an assignee, to avoid it being forgotten.
• Dismiss the suggestion if the changes are not suitable for templating.

You will need to dismiss this review before this PR can be merged. Recommend the reviewer does this as their final action before merging, as this text will continually update as commits come in.

Templated files

The following changed files are templated:

• pyproject.toml, templated by SciTools/.github/templates/pyproject.toml

Template candidates

The following changed files are not currently templated, but their parent directories suggest they may be good candidates for a new template to be created:

• docs/src/Makefile

Footnotes

1. Include this text in the PR body to avoid any notifications about applying the template changes back to the source repo!
   @scitools-templating: please no update notification on: iris ↩