* filer: stop isSameChunks from sorting caller-owned chunk slices
slices.SortFunc reorders the input in place. filer.remote.sync calls IsSameData on a metadata event's NewEntry inside isMetadataOnlyUpdate and later stamps the filer entry under an IF_ENTRY_EQUAL precondition carrying that same entry. The ETag-sorted chunk list never matches the stored entry, so every stamp of a multi-chunk object fails, synced_mtime_ns stays zero, and dirty objects are re-uploaded forever. Sort clones of the slices instead.
* filer: test IsSameData leaves input chunk order unchanged
Guards the clone-then-sort fix: a regression back to in-place sorting would reorder caller-owned chunk slices and reintroduce the remote-sync IF_ENTRY_EQUAL mismatch.
Hector Peeters