Editable installs broken with pip 22.1

# Problem

All CI jobs will probably fail right now if using `pip` 22.1 with the tell-tale error of:

```
pip._vendor.packaging.markers.UndefinedEnvironmentName: 'extra' does not exist in evaluation environment.
```

## References
- observed on #724
- probably due to https://github.com/pypa/pip/issues/11110
- it's suggested the "clever" `_version.py` and `version_info` stuff triggers `flit` to do more install than it's ready to do...

## Approaches

- wait for it to resolve itself
- `pip` or `flit` might fix something
- accept dupliaction
- in `pyproject.toml`
- remove `version` from `dynamic`
- add explicit version there
- add a test, etc. to verify the versions are in sync
- ???