Feature request: allow counting blank space at end of last line in `stri_wrap()`

https://github.com/gagolews/stringi/commit/c2dd9be19b5bc21690519040fd1fd23f619dc957 refactored the dynamic algorithm used by `stri_wrap()` to not count blank space at the end of the last line in a string. It would be great if there could be an option to re-enable counting the blank space, so one could create a string where each line, including the last, is as close to even as possible.

Start by reviewing the referenced commit and the stri_wrap() implementation to understand the current last-line width behavior. Add an option that restores counting trailing blank space on the final line, and confirm that both option modes produce the intended wrapping results with the project's existing tests.

Written by the indexing model from the issue text.