Improve `faq/design.rst` rst markup

[ezio-melotti]

I noticed that the faq/design.rst page has several parts that either have no markup (e.g. try/except, :=, etc.) or a generic ``...`` when a more specific one could be used (e.g. :c:type:`double`).

We should review the page and apply proper markup where applicable. Some other FAQs might need the same treatment.

• PR: [3.11] gh-96265: Formatting changes for faq/programming (GH-98242) #98991

• PR: [3.10] gh-96265: Formatting changes for faq/programming (GH-98242) #98994

[slateny]

Created a PR for just design.rst - as for other FAQs, I think the general faq could get some grave accents too (maybe under 'version numbering', A.B.C etc. could be literal), but changes to design.rst are looking somewhat long already so I'll put them in a separate PR.

Some of the missing formatting can also be found in other docs (i.e., ``if`` -> :keyword:`if`), should those be globally applied or should it change file-by-file?

[CAM-Gerlach]

File by file, I'd say, if we're going through them, unless that's the only change needed in the file