Feature request: Hasher, copy hashes on server-side copy (maybe simple copy too)

[disconnect5852]

i see that if i use the --hasher-auto-size and copying files in same remote, so rclone uses server-side copy, then the hashes aren't just copied to the new files, but re-hashing all.

I think copying the hashes is enough for server-side copy, as its very likely that the server verifies the copy. I don't know how rclone verifies the copies it not server-side, but maybe for those its enough too, or perhaps it should be chooseable with a command line flag to copy the hash, or re-hash on non server side copy