Three fixes for tests that fail locally but pass on CI:

1. binary_io: Switch COPY to \copy (client-side) so temp files are
   owned by the test runner, avoiding /tmp sticky-bit permission
   issues when the PG server creates files as a different user.

2. coverage: Use a shared temp directory with 777 permissions for
   server-side file writes (pageviz, dump). Add id tiebreaker to
   queries with tied BM25 scores for deterministic row ordering.

3. inheritance: Extend is_child_partition_index() to handle regular
   table inheritance. PG17's planner may choose a child table's
   index over the parent's; the validation hook now allows this
   when the tables have an inheritance relationship.