enh: Add backend argument to lazy

[MarcoGorelli]

Similar to #1888

I think lazy could have a backend: ModuleType | Implementation | LazyBackend argument, so all of the following could be supported:

df: nw.DataFrame
df.lazy('duckdb')
df.lazy(duckdb)
df.lazy(nw.Implementation.DUCKDB)

LazyBackend could be Literal['polars', 'dask', 'duckdb', 'pyspark']. There may be some combinations of eager to lazy backends on which we'd have to raise, but in most cases we can probably manage by going via PyArrow

Ultimately, I think

nw.from_dict(data, backend='pyarrow').lazy('duckdb')

would be pretty ergonomic and useful

[raisadz]

I would like to take this issue if no one else has started working on it yet