[FEA] Support polars.Expr.str.to_titlecase 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.to_titlecase. Running the example from the docs yields:

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

s = pl.Series(["01:00", "02:00", "03:00"])

df = pl.DataFrame(
    {
        "quotes": [
            "'e.t. phone home'",
            "you talkin' to me?",
            "to infinity,and BEYOND!",
        ]
    }
).lazy()
df = df.with_columns(
    quotes_title=pl.col("quotes").str.to_titlecase(),
)
res = df.collect(engine=engine)
print(res)

 NotImplementedError: String function <Name.Titlecase: 40>

Describe the solution you'd like
I'd like the above code to be able to execute using the polars GPU backend. At first glance this seems it may map nicely to cudf::strings::title.

Describe alternatives you've considered
N/A

Additional context
#16480