test: optional filters start in the post-scan filter in sqllogictests

With the adaptive filter placement, an optional filter starts in the
post-scan filter like a required conjunct, thus the `EXPLAIN ANALYZE`
metrics move from `pushdown_rows_*` and `predicate_cache_*` to
`post_scan_rows_*`. The results do not change.

PR: #25727

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: adriangb