Chore: format documentation examples

[findepi]

Format examples in doc strings.
Have the CI ensure all doc strings remain formatted.

rustfmt has an option for this

• https://rust-lang.github.io/rustfmt/?version=v1.8.0&search=#format_code_in_doc_comments

example

cargo fmt -- --config format_code_in_doc_comments=true

[CuteChuanChuan]

take

[alamb]

Copying a comment from #16916 (comment)

To assist us in reviewing, can you please break it up as follows:

1. Format individual crates (like datafusion and datafusion-datasource) or collections of crates (e.g. datafusion-functions-*) in individual PRs -- we will be much faster to review 10 200 line PRs than 1 2000 line PR I believe
2. A final PR that enables the CI check to ensure no new tests are added without formatting

Thank you !