Ban (or restrict) partial functions with hlint

[kostmo]

Ideally we don't want any instances of error in the codebase (https://github.com/swarm-game/swarm/pull/1484#discussion_r1315211065). For similar reasons, we should restrict use of partial functions like (!!), fromJust, and head to a vetted subset of modules. hlint can whitelist where certain functions may be used.

• [X] NonEmpty.fromList (#1503)
• [X] Prelude.head (#1503)
• [x] Prelude.tail
• [x] (!!)
• [ ] (Data.Map.!)
• [ ] error
• [x] fromJust
• [x] undefined

[byorgey]

It looks like we don't have any uses of fromJust, so we could just add that to the hlint config.

[xsebek]

There may be other more obscure functions - for example in tests, I use the sneaky (^?!). 🙂

[byorgey]

I'm not as concerned about tests, since those don't directly affect users if they crash. But yes, we should disallow (^?!) and its ilk.