Fix memory leaks in row filtering

[McFalljb]

Summary

Row filtering had two cleanup gaps. Filtered initial copies retained the tuple rebuilt for every scanned row. Streaming changes could also return after a rejected filter without releasing executor state or popping the active snapshot.

This change frees rebuilt tuples on both accepted and rejected initial-copy paths. It also defers the streaming filter result until after its executor and snapshot cleanup has completed.

The tuple reconstruction added in #387 is preserved, including correct handling of columns with atthasmissing.

Verification

I ran the same rejected-row initial-copy test against the original and patched builds using a 200,000-row table. Since no rows match, this isolates memory used while scanning and evaluating the filter from memory used to return matching rows.

Build	Returned rows	Initial backend RSS	Peak backend RSS	Growth
Original 9a0e182	0	16.5 MiB	223.1 MiB	206.5 MiB
Patched	0	11.0 MiB	24.6 MiB	13.6 MiB

Streaming row filter cleanup

pglogical_change_filter() returned immediately when a streaming row filter evaluated to false or SQL NULL. That skipped ExecDropSingleTupleTableSlot(), FreeExecutorState(), and PopActiveSnapshot(). The second commit records the filter result, performs that cleanup, and then returns it.

I tested both versions by decoding 200,000 inserts rejected by the same streaming row filter:

Build	Emitted inserts	Initial backend RSS	Peak backend RSS	Growth
Before streaming cleanup d94c19f	0	14.1 MiB	96.8 MiB	82.6 MiB
After streaming cleanup 056debd	0	17.0 MiB	46.8 MiB	29.8 MiB

I also verified that an accepting streaming filter emitted all 10 test inserts and that a filter evaluating to SQL NULL emitted none.

Additional initial-copy checks covered 100,000 partially accepted rows and 200,000 fully accepted rows. Each case returned the expected count. The post-ALTER TABLE default used to exercise the #387 behavior was also preserved for every returned row.

Supersedes #529, which GitHub closed when the source fork was deleted.

Fixes #477