Skip directory entries in RecursiveCopyableDataset to fix IOException on empty source dirs (#4181)

* [GOBBLIN-XXXX] Skip directory entries in RecursiveCopyableDataset to avoid IOException on empty source dirs

When source.path is an empty directory, FileListUtils.listFilesToCopyAtPath
(includeEmptyDirectories=true) returns the directory itself as the sole
FileStatus entry. The subsequent call to
resolveReplicatedOwnerAndPermissionsRecursively passes file.getPath().getParent()
as fromPath — which is *above* replacedPrefix — inverting the ancestry check
and throwing an IOException.

Skip FileStatus entries where isDirectory=true; empty source directories
produce no copy work units by design. Log a warning so operators can
diagnose misconfigured source paths.

* [ETL-19035] Fix ancestor path resolution for empty source directories in RecursiveCopyableDataset

When includeEmptyDirectories=true and the source root is empty, FileListUtils
returns the root directory itself as a FileStatus entry. Calling .getParent()
on it produces a path above replacedPrefix, breaking the ancestry check in
resolveReplicatedOwnerAndPermissionsRecursively.

Fix: guard with isAncestor(replacedPrefix, parentPath) — fall back to the
file's own path only when parentPath is above the dataset root. This preserves
correct ancestor permission replication for nested empty subdirs (where
.getParent() is still within replacedPrefix) and ensures the empty root
directory is replicated at the destination rather than skipped.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

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Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>