fix: updated imports for polars extension 1.0­.0

[zilto]

Polars upgrading to >= 1.0.0 introduced breaking changes, in particular going from polars.typing_aliases to polars._typing.

venv/lib/python3.11/site-packages/hamilton/plugins/polars_post_1_0_0_extension.py:597: DeprecationWarning: The polars.type_aliases module is deprecated. The type aliases have moved to the polars._typing module to explicitly mark them as private. Please define your own type aliases, or temporarily import from the polars._typing module. A public polars.typing module will be added in the future.
from polars.type_aliases import ColumnTotalsDefinition, RowTotalsDefinition

We made changes accordingly, but missed two imports that were within a materializer definition. The warning is triggered when the materializer is registered during extension loading. This explains why we missed it and it wasn't covered by our tests.

Also, I renamed polars_post_1_0_0_extension.py to the plural polars_post_1_0_0_extensions.py to match convention.

[elijahbenizzy]

Thanks for the fix