Filter/Agg transpose bugfix

[jurplel]

The check for whether or not a filter expression could be pushed beyond an agg node was incorrect.

It was checking if the column was in the group by columns (checking the equality of the numbers), when it should be checking based on indices if we are only referring to columns that are emitted from the agg node as group by columns.

For example, if we see:

Filter #1 > 100
    Agg { groups: [#1], agg: Sum() }

We should not push down because #1 refers to the sum column. In the current main branch, it is pushed down because it sees that #1 equals a column in the groups field. It should be checking that every column is < groups.len() instead.