Polars AVRO reader/writer

[skrawcz]

Implement https://pola-rs.github.io/polars/py-polars/html/reference/io.html#avro as a data saver/loader.

1. It should go into polars_extensions.py, one class for the writer, on class for the reader, e.g. much like how the polars csv reader and writer are structured.
2. There should be requisite tests to exercise the functionality. We can do one test that writes & then reads it's own output.
3. Then an example should be added to a new directory called materialization under example/polars. It should mirror the pandas materialization example in structure.
4. If there's an issue with type hints, let me know and we can chat through it.

[ghost]

Hi @skrawcz , I'll take this up.

[skrawcz]

merged. Thanks @kokobhara !

[skrawcz]

done in. (#447 )