updated syntax

[abstractqqq]

Now the crate has more up-to-date polars syntax, e.g.

import polars_istr as istr

df.select(
    istr.iban_country_code("iban_column")
)

which linters can understand. I also think we are ready for v0.1.0 release.

[ctdunc]

Looks good. Thank you for handling!