Proposed commit log message:
```
security/py-ecdsa: Update to 0.16.0
- Update to 0.16.0
- Add test target
- Pet portlint
Changelog:
https://github.com/warner/python-ecdsa/releases/tag/python-ecdsa-0.16.0
Reviewed_by: koobs
Approved by: koobs (ports, mentor, maintainer)
Differential_Revision: D27187
MFH: No (API changes, unclear on compatibility)
```