Extend the pending-directory collision test with absent recovery and a smaller
key. Add all six normal-object, directory, and pending-object channel orders,
checking complete-group recovery and preservation of trailing entries.
Test changes adapted from commit 557bc274a32330321fa5e5ac7636068c7bd98eb0.
Retain the complete-group directory handling from 3dd53eb81f.
Signed-off-by: Feng Ruohang <rh@vonng.com>