Remove seed setting and replace \dontrun{} with \donttest{}

[fukuhiro2023]

This PR updates:

• meta_sl_example() to remove seed setting.
• rtf_base_char_subgroup to replace \dontrun{} with \donttest{}.

Also, cran-comments.md is added.
These are based on the CRAN's feedback for v0.1.0 release as below:

\dontrun{} should only be used if the example really cannot be executed (e.g. because of missing additional software, missing API keys, ...) by the user. That's why wrapping examples in \dontrun{} adds the comment ("# Not run:") as a warning for the user. Does not seem necessary.
Please replace \dontrun with \donttest.
Only functions which are supposed to only run interactively (e.g. shiny) should be wrapped in if(interactive()). Please replace if(interactive()){} if possible.

Please do not set a seed to a specific number within a function. -> R/meta_sl_example.R

[wangben718]

Looks good to me. Please upload it again when you have time.