feat(rust): Add newline to Aggregate..FROM describe_optimization_plan

[owrior]

import polars as pl

df = pl.DataFrame({'a':[0,1],'b':[1,2]})

print(
df.lazy().groupby("a").agg(pl.col("b").mean()).describe_optimized_plan()
)

Now returns:

Aggregate
        [col("b").mean()] BY [col("a")] FROM
   DF ["a", "b"]; PROJECT 2/2 COLUMNS; SELECTION: "None"

Closes #5208

[ritchie46]

Thanks! It is almost there. We should only keep the indentation level.

[owrior]

Now returns this:

Aggregate
        [col("b").mean()] BY [col("a")] FROM
          DF ["a", "b"]; PROJECT 2/2 COLUMNS; SELECTION: "None"

[ritchie46]

There is an indent argument that should be used. See the other nodes.

The indentation changes when we get deeper in the query.

[owrior]

Does this look ok?

Output:

Aggregate
        [col("b").mean()] BY [col("a")] FROM
          DF ["a", "b"]; PROJECT 2/2 COLUMNS; SELECTION: "None"

[ritchie46]

So the first indentation is correct. But then there is a new line followed by a tab, e.g. \n\t that should also be indented by {:indent} instead of the tab.

"{:indent$}Aggregate\n{:indent}{:?} BY {:?} FROM",

[owrior]

Ahh yes sorry I completely missed that one. Think I've addressed this now.

[ritchie46]

That's it! Thanks.