`Deprecated` annotation

```py
a: Deprecated[int, message='Erm, I thought this was deprecated?', since='1.0.0', level='warning'] = 1
```

- from https://github.com/DetachHead/basedpyright/issues/48

Start by reading the provided annotation example and the linked basedpyright issue, then locate the existing annotation and runtime-handling entry points in the repository. Check how related annotations are tested and define what support for the message, since, and level arguments should mean; the issue names no target file or test, so scope needs maintainer confirmation.

Written by the indexing model from the issue text.