misc: bump to 0.12.0 [skip ci]

bump version

fix: better handling of columns with datatype `Null`

docs: fix readme formatting

tidypolars 0.9.0

Bump version number to 0.8.0

Bump to 0.7.0

Release 0.6.0

misc: bump to 0.5.0

misc: fix changes related to polars 0.11.0, prepare 0.4.0