cask/artifact: enable Sorbet `typed: strict` for abstract classes

Enable strict typing for the abstract base classes in `Cask::Artifact`:
- `AbstractArtifact`
- `AbstractFlightBlock`
- `AbstractUninstall`
- `Relocated`

This adds proper type signatures to all methods and updates the typing
level from `typed: true` to `typed: strict`.

Also marks `english_name` and `dirmethod` as `overridable` in
`AbstractArtifact` and adds `override` to subclasses that override them.

Advances https://github.com/Homebrew/brew/issues/17297