Include a polars backend?

[denehoffman]

Now that polars is out of v0, it would be nice to have some features to stream directly to polars dataframes. Currently it's not difficult to convert the library='np' output to a polars dataframe (pl.DataFrame(ttree.arrays(library='np')) usually does the trick), but it might be interesting to directly read to one, especially in cases where streaming and lazy evaluation become important (large files). Again, this is not a feature I need right now (or have the knowledge to write myself), just might be something to look at in the future.

[denehoffman]

I just realized this is very related to #1261, but it could also just be done through the py-polars frontend without any Rust involvement from the uproot side.

[jpivarski]

In fact, it's even more related to #1096. I should label this issue as a duplicate and you should follow up on #1096.