Render aggregates over expressions (e.g. sumBy(caseWhen …)) instead of throwing

[michaelglass]

whoops, one more bug from me...

sumBy/avgBy/etc. over anything other than a bare column threw Invalid argument to aggregate function — even though NAggregateColumn's own doc comment says such expressions should fall through to full expression rendering. So a conditional count like SUM(CASE WHEN … THEN 1 ELSE 0 END) was impossible.

AggregateColumn/NAggregateColumn now return None for a non-column argument, letting it render as an expression. The Option/Nullable .Value chain is unaffected — it's still matched by the Property arm.

Tests: sumBy/avgBy over caseWhen now render SUM(CASE WHEN …) / AVG(CASE WHEN …).

[JordanMarr]

    let sql =
        select {
            for p in production.product do
            groupBy p.color
            select (sumBy (caseWhen (p.standardcost > 100m) 1 0))
        }
        |> toSql

That select statement is doing some work lol