`{msg}` `.set_message(Cow<'static, str>)` design unnecessarily requires allocation about indicatif

[djc]

So are you updating the message on every iteration of a hot loop? Maybe it's feasible to use a ProgressTracker impl instead?

[djc]

Uh, no? The ProgressTracker can be used to define a custom key for use in a format string, so you can do whatever you need with your float and only have it format whenever indicatif is drawing.

[JulianKnodt]

Right now I'm displaying [Elapsed/ETA] {progress bar} {current iter}/{total iters}{msg}. I now only update the msg every Nth iteration, which is alright.

I don't see a ton of docs for the progress tracker (I didn't even know it existed). If I want to use that, do I have to drop a lot of existing functionality?