Filter pushdown selectivity threshold

## Summary

Skip pushing down row selection filters when the selection has low effectivity (selects nearly all rows), as the overhead of individual small skip/read calls during Parquet decoding can outweigh the benefit.

Related PR: #9414

Start by reviewing related PR #9414 and tracing the Parquet filter pushdown and decoding path. Identify how selection effectivity is measured and where a selectivity threshold can be applied; done means highly inclusive selections avoid costly individual skip/read calls without losing filtering benefits.

Written by the indexing model from the issue text.