Improve `NumLike` type errors

Missing a `HasDivision` instance has an unfortunate error message:
```
src/Test/Cardano/Ledger/Constrained/Conway/Instances/Ledger.hs:246:10: error: [GHC-18872]
    - Couldn't match type Word64 with EpochNo
        arising from the superclasses of an instance declaration
    - In the instance declaration for NumLike EpochNo
    |
246 | instance NumLike EpochNo
    |          ^^^^^^^^^^^^^^^
```