[FEA] Support `polars.Expr.str.normalize` in `cudf-polars`

[brandon-b-miller]

Is your feature request related to a problem? Please describe.
Today on branch-25.08, we lack support for polars.Expr.str.normalize. Running the example from the docs yields:

import polars as pl
engine = pl.GPUEngine(raise_on_fail=True)

df = pl.DataFrame({"text": ["01²", "ＫＡＤＯＫＡＷＡ"]}).lazy()
df = df.with_columns(
    nfc=pl.col("text").str.normalize("NFC"),
    nfkc=pl.col("text").str.normalize("NFKC"),
)

res = df.collect(engine=engine)
print(res)

NotImplementedError('String function <Name.Normalize: 22>

Describe the solution you'd like
I'd like the above code to be able to execute using the polars GPU backend. I don't see a feature or group of features in libcudf that would be an obvious way of computing the equivalent on the GPU, so we might have to build something somewhat from scratch to support this eventually.

Describe alternatives you've considered
N/A

Additional context
#16480

[davidwendt]

There is a character normalizer in cudf https://docs.rapids.ai/api/cudf/stable/user_guide/api_docs/character_normalizer/
It doesn't accept a unicode form but likely represents one of them by default (I don't know which).
In libcudf, this is implemented in the nvtext APIs: https://docs.rapids.ai/api/libcudf/stable/group__nvtext__normalize#ga7dcfac0c517d468a9b70303d9e0c1512