Improve `faq/design.rst` rst markup

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