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

**Is your feature request related to a problem? Please describe.**
Today on `branch-25.08`, we lack support for [polars.Expr.str.escape_regex](https://docs.pola.rs/api/python/stable/reference/expressions/api/polars.Expr.str.escape_regex.html). Running the example from the docs yields
```
import polars as pl
engine = pl.GPUEngine(raise_on_fail=True)

df = pl.DataFrame({"text": ["abc", "def", None, "abc(\\w+)"]}).lazy()
df = df.with_columns(pl.col("text").str.escape_regex().alias("escaped"))
res = df.collect(engine=engine)
print(res)
```

```
NotImplementedError: String function
```

**Describe the solution you'd like**
I'd like the above code to be able to execute using the polars GPU backend. I couldn't find a `libcudf` api that maps 1-1 to this feature, however it may be possible to compute this using some kind of particular `replace` operation.

**Describe alternatives you've considered**
N/A

**Additional context**
https://github.com/rapidsai/cudf/issues/16480