Prework

• Read and agree to the code of conduct and contributing guidelines.
• If there is already a relevant issue, whether open or closed, comment on the existing thread instead of posting a new issue.
• New features take time and effort to create, and they take even more effort to maintain. So if the purpose of the feature is to resolve a struggle you are encountering personally, please consider first posting a "trouble" or "other" issue so we can discuss your use case and search for existing solutions first.
• Format your code according to the tidyverse style guide.

Proposal

tar_poll() should be a continuously refreshing version of tar_progress_summary() (#380) in the R console. It will serve as a lightweight alternative to tar_watch(). (tar_watch() can be annoying sometimes because the graph takes a few seconds to refresh.)