Improve runtime and output of tests for replication slots checkpointing.
The TAP tests that verify logical and physical replication slot behavior during checkpoints (046_checkpoint_logical_slot.pl and 047_checkpoint_physical_slot.pl) inserted two batches of 2 million rows each, generating approximately 520 MB of WAL. On slow machines, or when compiled with '-DRELCACHE_FORCE_RELEASE -DCATCACHE_FORCE_RELEASE', this caused the tests to run for 8-9 minutes and occasionally time out, as seen on the buildfarm animal prion.
Quite a few animals have started failing since this commit (for example [1]) . I haven't looked into why, but I suspect something is wrong.
stderr:
# Failed test 'Logical slot still valid'
# at /home/bf/bf-build/flaviventris/HEAD/pgsql/src/test/recovery/t/046_checkpoint_logical_slot.pl line 134.
# got: 'death by signal at /home/bf/bf-build/flaviventris/HEAD/pgsql/src/test/perl/PostgreSQL/Test/Cluster.pm line 181.
# '
# expected: ''
I see this failing on my fork's CI, so it seems like it could have been caught earlier?
