Turn off CSE for new streaming engine

[orlp]

CSE can cause with_columns to be generated for common subexpressions with the wrong length, e.g. for

df.select(pl.col.x.explode().filter(pl.col.x.explode() < 5)

In the new streaming engine this is illegal, so the current CSE should be turned off for it. We'll later add CSE at the physical plan level for the new streaming engine.