Formatter: `TypeAlias`

See [PEP 695](https://peps.python.org/pep-0695/) for details on this python 3.12 feature. Not to be confused with `typing.TypeAlias` of python 3.10. The goal is to format statements in the form:

```python
# TypeAlias
type ListOrSet[T] = list[T] | set[T]
```