Do not bypass `auto_duplicate()` even when just modifying meta-data

[cbrnr]

auto_duplicate() protects file-backed data sets by always duplicating before a mutation, and asks Create-new-vs-Overwrite for derived ones. At least three actions skip this and mutate self.current directly:

• channel_properties()
• rename_channels()
• find_events()

So renaming a channel or running Find Events right after loading a file silently mutates the root data set that's supposed to represent that file untouched. I suggest running these (and any other actions with similar behavior) through auto_duplicate() like every other processing action.