Allow write mode in rich.progress.Progress.open()

[jordi-torrents]

Right now you can display the reading process of a file by using rich.progress.Progress.open() in read mode. This gives you the fraction of the file being loaded from the disk. It's cool.

Then, it would be natural to ask for open() to allow also write mode. The task would not have a total value but it could still show the amount of bytes being writen and the writting speed. I went into the code and saw that it was explicitly forbiden by raising an UnsupportedOperation("write") exception in the rich.progress._Reader.write() method.

I adapted these classes in my project here and I managed them to also allow writting. It works beautifully. I haven't tested on many different scenarios but there seems to exist a simple solution with a simple implementation for writting.

So, why isn't writting allowed in the first place? Am I missing something? Would you be up for a PR to add write mode in rich.progress.Progress.open()?