Replace hacky `.progress` bar with official progressr machinery

[DavisVaughan]

See discussion in #305, in particular the ideal solution would be #305 (comment) where progressr::handlers(global = TRUE) could be set as the default during progressr's package startup process.

This would mean that future_map(x, fn, .progress = TRUE) that just signals progression conditions as #305 does would show a progress bar to users by default without them having to do anything else (maintaining nice backwards compat with old furrr behavior).

[dpprdan]

• Some other option?

Replace with cli progress bars, to stay in sync with purrr?

[DavisVaughan]

Likely some internal usage of progressr, possibly with a cli default, but yea now that purrr added the progress option back in I am inclined to keep it

[statzhero]

The purrr progress bar is one of my favorites, so I hope furrr can align it as much as possible. I appreciate all your work and was wondering what the plan to maintain furrr is?