Apply Sourcery suggestions and fix typos

[DimitriPapadopoulos]

• Start applying Sourcery suggestions.
• Fix typos.

TODO:

• Add unit tests and/or doctests in docstrings
• Add docstrings and API docs for any new/modified user-facing classes and functions
• New/modified features documented in docs/user-guide/*.rst
• Changes documented as a new file in changes/
• GitHub Actions have all passed
• Test coverage is 100% (Codecov passes)

[dstansby]

I'm 👍 for spelling fixes, and 👎 for refactoring without a linter doing it automatically for us (because it just creates PR review noise for not much technical debt reduction). Could you open a PR to repalce this that just includes the spelling fixes?

[DimitriPapadopoulos]

I think Sourcery applies linter rules, but rules that might not be part of ruff (yet). More importantly, I think Sourcery is a good addition - AI assistance for PR review. But I understand you don't agree with it.

Some of the Sourcery suggestions do improve source code, such as:

-    n_ellipsis = sum(1 for i in selection if i is Ellipsis)
+    n_ellipsis = selection.count(Ellipsis)

How about keeping the couple changes that really make sense?