Rewrite COUNT over non-nullable columns to COUNT(1)

[wudidapaopao]

Is your feature request related to a problem or challenge?

COUNT(non_nullable_column) counts every row, but DataFusion still evaluates and reads the column unnecessarily.

Describe the solution you'd like

Rewrite safe, non-DISTINCT counts during logical simplification:

COUNT(non_nullable_column) -> COUNT(1)

Preserve the original output name and schema. For multi-argument COUNT, rewrite only when every argument is provably non-null.

Additional context

Split from #25849 as suggested in #25849 (comment).

[wudidapaopao]

take