Poland subdivision codes should be numeric

[lanarowe]

Poland's subdivisions used alphabetical codes like PL-SL until November 2018, when they changed to numeric subdivision codes like PL-24 (see https://en.wikipedia.org/wiki/ISO_3166-2:PL). This package is still using the old codes.

[pariz]

Hi, thank you for the information. I am currently working on a new version of countries that will keep a more up to date data set (that will not need manual maintenance), i'm going to link to it from this repo somewhere in the beginning of 2025.

[oleg-balunenko-gismart]

@pariz Hi
Are there any updates on the planned changes for the new version?