Consider using `fast_unnest_character()` to unnest list columns

[toph-allen]

The function fast_unnest_character() was added in #404 to unnest list columns while treating them as character vectors.

There are other places in connectapi where list columns are emitted; we could consider unnesting them using this function.

(From @nealrichardson’s comment on that pull request: https://github.com/posit-dev/connectapi/pull/404/files#r2210180449)

[toph-allen]

Closing, as this function was removed.