Use mypy in boefjes, octopoes and rocky

[dekkers]

Currently mypy is excluded in boefjes, octopoes and rocky. We should also do type checking there because it can find bugs such as #2115. There are a lot of errors, but most look easy to fix. If some typing problems are hard to fix we can also use Any or ask mypy to ignore things because that would be better than not running mypy at all.