0.20.0 release

[eitsupi]

We have not incorporated polars 0.43.1-rs but hope to release it soon, as testing has begun to fail (#1257).

@etiennebacher Thoughts?
(For now, I ran the library release workflow, but it is OK to undo it later.)

[etiennebacher]

Didn't we include 0.43.1 in #1230?

I don't have anything specific on my radar for now. I thought we could include the next rust-polars release in 0.20.0 since the changelog is a bit sparse, but I don't have a problem with releasing 0.20.0 now. Then maybe the next release post-rewrite will be 1.0?

[eitsupi]

Didn't we include 0.43.1 in #1230?

My bad, you are right.

Then maybe the next release post-rewrite will be 1.0?

That makes sense, since it is certainly a pretty huge breaking change.
And, it is natural to use something like v1 for the new default branch name and change the current main branch to something like v0 (the strategy followed by docker compose).

But I'm not sure if using 1.0 here is a good thing since 1.0 is generally meant to be stable, though Python Polars will be versioned up to v2 and v3 with major releases every 3 to 6 months, so it is consistent.

[etiennebacher]

Alright, let's discuss that later then ;) For now we can release 0.20.0

[eitsupi]

Done via #1259