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

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

df = pl.DataFrame({"text": ["foo", "bar", "mañana"]}).lazy()
df = df.with_columns(pl.col("text").str.reverse().alias("reversed"))
res = df.collect(engine=engine)
print(res)

 NotImplementedError: String function <Name.Reverse: 27>

Describe the solution you'd like
I'd like the above code to be able to execute using the polars GPU backend. This API should map 1-1 to cudf::strings::reverse.

Describe alternatives you've considered
N/A

Additional context
#16480