Make Hubris archives Clone

[labbott]

In at least one spot in humility this is a significant performance win

[mkeeter]

Can you say more about why this helps? I'm nervous for two reasons:

• Cloning an object that contains a Vec<..> is a code smell, because it has to reallocate and copy. I normally try to use an Arc instead (either wrapping the entire struct or converting the Vec<u8> to an Arc<[u8]>).
• The RawHubrisArchive can be edited and then used to overwrite the original file. The overwrite function consumes the object; this is an API choice to make it harder to misuse. If the object can be cloned, it's easier to mess stuff up – multiple functions could have RawHubrisArchive handles, perform different edits, and the last overwrite call would win.

[mkeeter]

Update: I put a few comments in oxidecomputer/humility#633, because I think we can avoid cloning the archive altogether.

[labbott]

Yep very good reasons not to do the clone and it turns out we don't need it