support datasets with different shapes

[BinYangOptics]

Currently, dexp commands such as stablize and copy only takes datasets with the same exact shape (except for time dimension).
It would be nice to support datasets with different shapes.

[JoOkuma]

The dataset supports different shapes because it indexed by the channel, but the command-line interface currently is limited to a single slicing, which could lead to issues when the data have different shapes.

If the CLI supported multiple slices and somehow mapped into their respective channel before processing, would it solve your problem?