testsuite: filtering coverage at depth

testsuite: filtering coverage at depth

Assert exactly which entries are/aren't transferred, deep in the tree:

  filter-depth      --exclude/--include precedence on files at every level, and
                    a -F per-directory .rsync-filter loaded from a deep dir that
                    applies to that subtree only (not above it).
  cvs-exclude       -C built-in cruft patterns (*.o, *~) at every level plus a
                    deep per-directory .cvsignore scoped to its subtree.
  size-filter       --max-size / --min-size select the right files all the way
                    down.
  files-from-depth  --files-from selects only the listed deep paths (implied
                    parents created); --from0 NUL-delimited; --exclude-from /
                    --include-from filter at depth.

(--existing / --ignore-existing are covered in delete-deep_test.py.)
Green on master and under --protocol=29/30.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>